EQUAL-STYLED AND RED-FLOWERED VAR.

I have described in my paper ‘On the Illegitimate Unions of Dimorphic and Trimorphic Plants’ this remarkable variety, which was sent to me from Edinburgh by Mr. J. Scott. It possessed a pistil proper to the long-styled form, and stamens proper to the short-styled form; so that it had lost the heterostyled or dimorphic character common to most of the species of the genus, and may be compared with an hermaphrodite form of a bisexual animal. Consequently the pollen and stigma of the same flower are adapted for complete mutual fertilisation, instead of its being necessary that pollen should be brought from one form to another, as in the common cowslip. From the stigma and anthers standing nearly on the same level, the flowers are perfectly self-fertile when insects are excluded. Owing to the fortunate existence of this variety, it is possible to fertilise its flowers in a legitimate manner with their own pollen, and to cross other flowers in a legitimate manner with pollen from another variety or fresh stock. Thus the offspring from both unions can be compared quite fairly, free from any doubt from the injurious effects of an illegitimate union.

The plants on which I experimented had been raised during two successive generations from spontaneously self-fertilised seeds produced by plants under a net; and as the variety is highly self-fertile, its progenitors in Edinburgh may have been self-fertilised during some previous generations. Several flowers on two of my plants were legitimately crossed with pollen from a short-styled common cowslip growing almost wild in my orchard; so that the cross was between plants which had been subjected to considerably different conditions. Several other flowers on the same two plants were allowed to fertilise themselves under a net; and this union, as already explained, is a legitimate one.

The crossed and self-fertilised seeds thus obtained were sown thickly on the opposite sides of three pots, and the seedlings thinned, so that an equal number were left on the two sides. The seedlings during the first year were nearly equal in height, excepting in Pot 3, Table 6/94, in which the self-fertilised plants had a decided advantage. In the autumn the plants were bedded out, in their pots; owing to this circumstance, and to many plants growing in each pot, they did not flourish, and none were very productive in seeds. But the conditions were perfectly equal and fair for both sides. In the following spring I record in my notes that in two of the pots the crossed plants are “incomparably the finest in general appearance,” and in all three pots they flowered before the self-fertilised. When in full flower the tallest flower-stem on each side of each pot was measured, and the number of the flower-stems on both sides counted, as shown in Table 6/94. The plants were left uncovered, and as other plants were growing close by, the flowers no doubt were crossed by insects. When the capsules were ripe they were gathered and counted, and the result is likewise shown in Table 6/94.

TABLE 6/94. Primula veris (equal-styled, red-flowered variety).

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Height of tallest flower-stem: crossed Plants.

Column 3: Number of Flower-stems: crossed Plants.

Column 4: Number of good capsules: crossed Plants.

Column 5: Height of tallest flower-stem: self-fertilised Plants.

Column 6: Number of Flower-stems: self-fertilised Plants.

Column 7: Number of good capsules: self-fertilised Plants.

Pot 1 : 10 : 14 : 163 : 6 4/8 : 6 : 6.

Pot 2 : 8 4/8 : 12 : * : 5 : 2 : 0.
*Several, not counted.

Pot 3 : 7 4/8 : 7 : 43 : 10 4/8 : 5 : 26.

Totals : 26.0 : 33 : 206 : 22.0 : 13 : 32.

The average height of the three tallest flower-stems on the crossed plants is 8.66 inches, and that of the three on the self-fertilised plants 7.33 inches; or as 100 to 85.

All the crossed plants together produced thirty-three flower-stems, whilst the self-fertilised bore only thirteen. The number of the capsules were counted only on the plants in Pots 1 and 3, for the self-fertilised plants in Pot 2 produced none; therefore those on the crossed plants on the opposite side were not counted. Capsules not containing any good seeds were rejected. The crossed plants in the above two pots produced 206, and the self-fertilised in the same pots only 32 capsules; or as 100 to 15. Judging from the previous generations, the extreme unproductiveness of the self-fertilised plants in this experiment was wholly due to their having been subjected to unfavourable conditions, and to severe competition with the crossed plants; for had they grown separately in good soil, it is almost certain that they would have produced a large number of capsules. The seeds were counted in twenty capsules from the crossed plants, and they averaged 24.75; whilst in twenty capsules from the self-fertilised plants the average was 17.65; or as 100 to 71. Moreover, the seeds from the self-fertilised plants were not nearly so fine as those from the crossed plants. If we consider together the number of capsules produced and the average number of contained seeds, the fertility of the crossed plants to the self-fertilised plants was as 100 to 11. We thus see what a great effect, as far as fertility is concerned, was produced by a cross between the two varieties, which had been long exposed to different conditions, in comparison with self-fertilisation; the fertilisation having been in both cases of the legitimate order.

Primula sinensis.

As the Chinese primrose is a heterostyled or dimorphic plant, like the common cowslip, it might have been expected that the flowers of both forms when illegitimately fertilised with their own pollen or with that from flowers on another plant of the same form, would have yielded less seed than the legitimately crossed flowers; and that the seedlings raised from illegitimately self-fertilised seeds would have been somewhat dwarfed and less fertile, in comparison with the seedlings from legitimately crossed seeds. This holds good in relation to the fertility of the flowers; but to my surprise there was no difference in growth between the offspring from a legitimate union between two distinct plants, and from an illegitimate union whether between the flowers on the same plant, or between distinct plants of the same form. But I have shown, in the paper before referred to, that in England this plant is in an abnormal condition, such as, judging from analogous cases, would tend to render a cross between two individuals of no benefit to the offspring. Our plants have been commonly raised from self-fertilised seeds; and the seedlings have generally been subjected to nearly uniform conditions in pots in greenhouses. Moreover, many of the plants are now varying and changing their character, so as to become in a greater or less degree equal-styled, and in consequence highly self-fertile. From the analogy of Primula veris there can hardly be a doubt that if a plant of Primula sinensis could have been procured direct from China, and if it had been crossed with one of our English varieties, the offspring would have shown wonderful superiority in height and fertility (though probably not in the beauty of their flowers) over our ordinary plants.

My first experiment consisted in fertilising many flowers on long-styled and short-styled plants with their own pollen, and other flowers on the same plants with pollen taken from distinct plants belonging to the same form; so that all the unions were illegitimate. There was no uniform and marked difference in the number of seeds obtained from these two modes of self-fertilisation, both of which were illegitimate. The two lots of seeds from both forms were sown thickly on opposite sides of four pots, and numerous plants thus raised. But there was no difference in their growth, excepting in one pot, in which the offspring from the illegitimate union of two long-styled plants exceeded in a decided manner in height the offspring of flowers on the same plants fertilised with their own pollen. But in all four pots the plants raised from the union of distinct plants belonging to the same form, flowered before the offspring from the self-fertilised flowers.

Some long-styled and short-styled plants were now raised from purchased seeds, and flowers on both forms were legitimately crossed with pollen from a distinct plant; and other flowers on both forms were illegitimately fertilised with pollen from the flowers on the same plant. The seeds were sown on opposite sides of Pots 1 to 4 in Table 6/95; a single plant being left on each side. Several flowers on the illegitimate long-styled and short-styled plants described in the last paragraph, were also legitimately and illegitimately fertilised in the manner just described, and their seeds were sown in Pots 5 to 8 in the same table. As the two sets of seedlings did not differ in any essential manner, their measurements are given in a single table. I should add that the legitimate unions in both cases yielded, as might have been expected, many more seeds than the illegitimate unions. The seedlings whilst half-grown presented no difference in height on the two sides of the several pots. When fully grown they were measured to the tips of their longest leaves, and the result is given in Table 6/95.

TABLE 6/95. Primula sinensis.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Plants from legitimately Crossed seeds.

Column 3: Plants from illegitimately Self-fertilised seeds.

Pot 1 : 8 2/8 : 8. From short-styled mother.

Pot 2 : 7 4/8 : 8 5/8. From short-styled mother.

Pot 3 : 9 5/8 : 9 3/8. From long-styled mother.

Pot 4 : 8 4/8 : 8 2/8. From long-styled mother.

Pot 5 : 9 3/8 : 9. From illegitimate short-styled mother.

Pot 6 : 9 7/8 : 9 4/8. From illegitimate short-styled mother.

Pot 7 : 8 4/8 : 9 4/8. From illegitimate long-styled mother.

Pot 8 : 10 4/8 : 10. From illegitimate long-styled mother.

Total : 72.13 : 72.25.

In six out of the eight pots the legitimately crossed plants exceeded in height by a trifle the illegitimately self-fertilised plants; but the latter exceeded the former in two of the pots in a more strongly marked manner. The average height of the eight legitimately crossed plants is 9.01, and that of the eight illegitimately self-fertilised 9.03 inches, or as 100 to 100.2. The plants on the opposite sides produced, as far as could be judged by the eye, an equal number of flowers. I did not count the capsules or the seeds produced by them; but undoubtedly, judging from many previous observations, the plants derived from the legitimately crossed seeds would have been considerably more fertile than those from the illegitimately self-fertilised seeds. The crossed plants, as in the previous case, flowered before the self-fertilised plants in all the pots except in Pot 2, in which the two sides flowered simultaneously; and this early flowering may, perhaps, be considered as an advantage.

27. POLYGONEAE.—Fagopyrum esculentum.

This plant was discovered by Hildebrand to be heterostyled, that is, to present, like the species of Primula, a long-styled and a short-styled form, which are adapted for reciprocal fertilisation. Therefore the following comparison of the growth of the crossed and self-fertilised seedlings is not fair, for we do not know whether the difference in their heights may not be wholly due to the illegitimate fertilisation of the self-fertilised flowers.

I obtained seeds by legitimately crossing flowers on long-styled and short-styled plants, and by fertilising other flowers on both forms with pollen from the same plant. Rather more seeds were obtained by the former than by the latter process; and the legitimately crossed seeds were heavier than an equal number of the illegitimately self-fertilised seeds, in the ratio of 100 to 82. Crossed and self-fertilised seeds from the short-styled parents, after germinating on sand, were planted in pairs on the opposite sides of a large pot; and two similar lots of seeds from long-styled parents were planted in a like manner on the opposite sides of two other pots. In all three pots the legitimately crossed seedlings, when a few inches in height, were taller than the self-fertilised; and in all three pots they flowered before them by one or two days. When fully grown they were all cut down close to the ground, and as I was pressed for time, they were placed in a long row, the cut end of one plant touching the tip of another, and the total length of the legitimately crossed plants was 47 feet 7 inches, and of the illegitimately self-fertilised plants 32 feet 8 inches. Therefore the average height of the fifteen crossed plants in all three pots was 38.06 inches, and that of the fifteen self-fertilised plants 26.13 inches; or as 100 to 69.

28. CHENOPODIACEAE.—Beta vulgaris.

A single plant, no others growing in the same garden, was left to fertilise itself, and the self-fertilised seeds were collected. Seeds were also collected from a plant growing in the midst of a large bed in another garden; and as the incoherent pollen is abundant, the seeds of this plant will almost certainly have been the product of a crossed between distinct plants by means of the wind. Some of the two lots of seeds were sown on the opposite sides of two very large pots; and the young seedlings were thinned, so that an equal but considerable number was left on the two sides. These plants were thus subjected to very severe competition, as well as to poor conditions. The remaining seeds were sown out of doors in good soil in two long and not closely adjoining rows, so that these seedlings were placed under favourable conditions, and were not subjected to any mutual competition. The self-fertilised seeds in the open ground came up very badly; and on removing the soil in two or three places, it was found that many had sprouted under ground and had then died. No such case had been observed before. Owing to the large number of seedlings which thus perished, the surviving self-fertilised plants grew thinly in the row, and thus had an advantage over the crossed plants, which grew very thickly in the other row. The young plants in the two rows were protected by a little straw during the winter, and those in the two large pots were placed in the greenhouse.

There was no difference between the two lots in the pots until the ensuing spring, when they had grown a little, and then some of the crossed plants were finer and taller than any of the self-fertilised. When in full flower their stems were measured, and the measurements are given in Table 6/96.

TABLE 6/96. Beta vulgaris.

Heights of flower stems measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 34 6/8 : 36. Pot 1 : 30 : 20 1/8. Pot 1 : 33 6/8 : 32 2/8. Pot 1 : 34 4/8 : 32.

Pot 2 : 42 3/8 : 42 1/8. Pot 2 : 33 1/8 : 26 4/8. Pot 2 : 31 2/8 : 29 2/8. Pot 2 : 33 : 20 2/8.

Total : 272.75 : 238.50.

The average height of the eight crossed plants is here 34.09, and that of the eight self-fertilised plants 29.81; or as 100 to 87.

With respect to the plants in the open ground, each long row was divided into half, so as to diminish the chance of any accidental advantage in one part of either row; and the four tallest plants in the two halves of the two rows were carefully selected and measured. The eight tallest crossed plants averaged 30.92, and the eight tallest self-fertilised 30.7 inches in height, or as 100 to 99; so that they were practically equal. But we should bear in mind that the trial was not quite fair, as the self-fertilised plants had a great advantage over the crossed in being much less crowded in their own row, owing to the large number of seeds which had perished under ground after sprouting. Nor were the lots in the two rows subjected to any mutual competition.

29. CANNACEAE.—Canna warscewiczi.

In most or all the species belonging to this genus, the pollen is shed before the flower expands, and adheres in a mass to the foliaceous pistil close beneath the stigmatic surface. As the edge of this mass generally touches the edge of the stigma, and as it was ascertained by trials purposely made that a very few pollen-grains suffice for fertilisation, the present species and probably all the others of the genus are highly self-fertile. Exceptions occasionally occur in which, from the stamen being slightly shorter than usual, the pollen is deposited a little beneath the stigmatic surface, and such flowers drop off unimpregnated unless they are artificially fertilised. Sometimes, though rarely, the stamen is a little longer than usual, and then the whole stigmatic surface gets thickly covered with pollen. As some pollen is generally deposited in contact with the edge of the stigma, certain authors have concluded that the flowers are invariably self-fertilised. This is an extraordinary conclusion, for it implies that a great amount of pollen is produced for no purpose. On this view, also, the large size of the stigmatic surface is an unintelligible feature in the structure of the flower, as well as the relative position of all the parts, which is such that when insects visit the flowers to suck the copious nectar, they cannot fail to carry pollen from one flower to another. (6/7. Delpino has described ‘Bot. Zeitung’ 1867 page 277 and ‘Scientific Opinion’ 1870 page 135, the structure of the flowers in this genus, but he was mistaken in thinking that self-fertilisation is impossible, at least in the case of the present species. Dr. Dickie and Professor Faivre state that the flowers are fertilised in the bud, and that self-fertilisation is inevitable. I presume that they were misled by the pollen being deposited at a very early period on the pistil: see ‘Journal of Linnean Society Botany’ volume 10 page 55 and ‘Variabilité des Espèces’ 1868 page 158.)

According to Delpino, bees eagerly visit the flowers in North Italy, but I have never seen any insect visiting the flowers of the present species in my hothouse, although many plants grew there during several years. Nevertheless these plants produced plenty of seed, as they likewise did when covered by a net; they are therefore fully capable of self-fertilisation, and have probably been self-fertilised in this country for many generations. As they are cultivated in pots, and are not exposed to competition with surrounding plants, they have also been subjected for a considerable time to somewhat uniform conditions. This, therefore, is a case exactly parallel with that of the common pea, in which we have no right to expect much or any good from intercrossing plants thus descended and thus treated; and no good did follow, excepting that the cross-fertilised flowers yielded rather more seeds than the self-fertilised. This species was one of the earlier ones on which I experimented, and as I had not then raised any self-fertilised plants for several successive generations under uniform conditions, I did not know or even suspect that such treatment would interfere with the advantages to be gained from a cross. I was therefore much surprised at the crossed plants not growing more vigorously than the self-fertilised, and a large number of plants were raised, notwithstanding that the present species is an extremely troublesome one to experiment on. The seeds, even those which have been long soaked in water, will not germinate well on bare sand; and those that were sown in pots (which plan I was forced to follow) germinated at very unequal intervals of time; so that it was difficult to get pairs of the same exact age, and many seedlings had to be pulled up and thrown away. My experiments were continued during three successive generations; and in each generation the self-fertilised plants were again self-fertilised, their early progenitors in this country having probably been self-fertilised for many previous generations. In each generation, also, the crossed plants were fertilised with pollen from another crossed plant.

Of the flowers which were crossed in the three generations, taken together, a rather larger proportion yielded capsules than did those which were self-fertilised. The seeds were counted in forty-seven capsules from the crossed flowers, and they contained on an average 9.95 seeds; whereas forty-eight capsules from the self-fertilised flowers contained on an average 8.45 seeds; or as 100 to 85. The seeds from the crossed flowers were not heavier, on the contrary a little lighter, than those from the self-fertilised flowers, as was thrice ascertained. On one occasion I weighed 200 of the crossed and 106 of the self-fertilised seeds, and the relative weight of an equal number was as 100 for the crossed to 101.5 for the self-fertilised. With other plants, when the seeds from the self-fertilised flowers were heavier than those from the crossed flowers, this appeared to be due generally to fewer having been produced by the self-fertilised flowers, and to their having been in consequence better nourished. But in the present instance the seeds from the crossed capsules were separated into two lots,—namely, those from the capsules containing over fourteen seeds, and those from the capsules containing under fourteen seeds, and the seeds from the more productive capsules were the heavier of the two; so that the above explanation here fails.

As pollen is deposited at a very early age on the pistil, generally in contact with the stigma, some flowers whilst still in bud were castrated for my first experiment, and were afterwards fertilised with pollen from a distinct plant. Other flowers were fertilised with their own pollen. From the seeds thus obtained, I succeeded in rearing only three pairs of plants of equal age. The three crossed plants averaged 32.79 inches, and the three self-fertilised 32.08 inches in height; so that they were nearly equal, the crossed having a slight advantage. As the same result followed in all three generations, it would be superfluous to give the heights of all the plants, and I will give only the averages.

In order to raise crossed and self-fertilised plants of the second generation, some flowers on the above crossed plants were crossed within twenty-four hours after they had expanded with pollen from a distinct plant; and this interval would probably not be too great to allow of cross-fertilisation being effectual. Some flowers on the self-fertilised plants of the last generation were also self-fertilised. From these two lots of seeds, ten crossed and twelve self-fertilised plants of equal ages were raised; and these were measured when fully grown. The crossed averaged 36.98, and the self-fertilised averaged 37.42 inches in height; so that here again the two lots were nearly equal; but the self-fertilised had a slight advantage.

In order to raise plants of the third generation, a better plan was followed, and flowers on the crossed plants of the second generation were selected in which the stamens were too short to reach the stigmas, so that they could not possibly have been self-fertilised. These flowers were crossed with pollen from a distinct plant. Flowers on the self-fertilised plants of the second generation were again self-fertilised. From the two lots of seeds thus obtained, twenty-one crossed and nineteen self-fertilised plants of equal age, and forming the third generation, were raised in fourteen large pots. They were measured when fully grown, and by an odd chance the average height of the two lots was exactly the same, namely, 35.96 inches; so that neither side had the least advantage over the other. To test this result, all the plants on both sides in ten out of the above fourteen pots were cut down after they had flowered, and in the ensuing year the stems were again measured; and now the crossed plants exceeded by a little (namely, 1.7 inches) the self-fertilised. They were again cut down, and on their flowering for the third time, the self-fertilised plants had a slight advantage (namely, 1.54 inches) over the crossed. Hence the result arrived at with these plants during the previous trials was confirmed, namely, that neither lot had any decided advantage over the other. It may, however, be worth mentioning that the self-fertilised plants showed some tendency to flower before the crossed plants: this occurred with all three pairs of the first generation; and with the cut down plants of the third generation, a self-fertilised plant flowered first in nine out of the twelve pots, whilst in the remaining three pots a crossed plant flowered first.

If we consider all the plants of the three generations taken together, the thirty-four crossed plants average 35.98, and the thirty-four self-fertilised plants 36.39 inches in height; or as 100 to 101. We may therefore conclude that the two lots possessed equal powers of growth; and this I believe to be the result of long-continued self-fertilisation, together with exposure to similar conditions in each generation, so that all the individuals had acquired a closely similar constitution.

30. GRAMINACEAE.—Zea mays.

This plant is monoecious, and was selected for trial on this account, no other such plant having been experimented on. (6/8. Hildebrand remarks that this species seems at first sight adapted to be fertilised by pollen from the same plant, owing to the male flowers standing above the female flowers; but practically it must generally be fertilised by pollen from another plant, as the male flowers usually shed their pollen before the female flowers are mature: ‘Monatsbericht der K. Akad.’ Berlin October 1872 page 743.) It is also anemophilous, or is fertilised by the wind; and of such plants only the common beet had been tried. Some plants were raised in the greenhouse, and were crossed with pollen taken from a distinct plant; and a single plant, growing quite separately in a different part of the house, was allowed to fertilise itself spontaneously. The seeds thus obtained were placed on damp sand, and as they germinated in pairs of equal age were planted on the opposite sides of four very large pots; nevertheless they were considerably crowded. The pots were kept in the hothouse. The plants were first measured to the tips of their leaves when only between 1 and 2 feet in height, as shown in Table 6/97.

TABLE 6/97. Zea mays.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 23 4/8 : 17 3/8. Pot 1 : 12 : 20 3/8. Pot 1 : 21 : 20.

Pot 2 : 22 : 20. Pot 2 : 19 1/8 : 18 3/8. Pot 2 : 21 4/8 : 18 5/8.

Pot 3 : 22 1/8 : 18 5/8. Pot 3 : 20 3/8 : 15 2/8. Pot 3 : 18 2/8 : 16 4/8. Pot 3 : 21 5/8 : 18. Pot 3 : 23 2/8 : 16 2/8.

Pot 4 : 21 : 18. Pot 4 : 22 1/8 : 12 6/8. Pot 4 : 23 : 15 4/8. Pot 4 : 12 : 18.

Total : 302.88 : 263.63.

The fifteen crossed plants here average 20.19, and the fifteen self-fertilised plants 17.57 inches in height; or as 100 to 87. Mr. Galton made a graphical representation, in accordance with the method described in the introductory chapter, of the above measurements, and adds the words “very good” to the curves thus formed.

Shortly afterwards one of the crossed plants in Pot 1 died; another became much diseased and stunted; and the third never grew to its full height. They seemed to have been all injured, probably by some larva gnawing their roots. Therefore all the plants on both sides of this pot were rejected in the subsequent measurements. When the plants were fully grown they were again measured to the tips of the highest leaves, and the eleven crossed plants now averaged 68.1, and the eleven self-fertilised plants 62.34 inches in height; or as 100 to 91. In all four pots a crossed plant flowered before any one of the self-fertilised; but three of the plants did not flower at all. Those that flowered were also measured to the summits of the male flowers: the ten crossed plants averaged 66.51, and the nine self-fertilised plants 61.59 inches in height; or as 100 to 93.

A large number of the same crossed and self-fertilised seeds were sown in the middle of the summer in the open ground in two long rows. Very much fewer of the self-fertilised than of the crossed plants produced flowers; but those that did flower, flowered almost simultaneously. When fully grown the ten tallest plants in each row were selected and measured to the tips of their highest leaves, as well as to the summits of their male flowers. The crossed averaged to the tips of their leaves 54 inches in height, and the self-fertilised 44.65, or as 100 to 83; and to the summits of their male flowers, 53.96 and 43.45 inches; or as 100 to 80.

Phalaris canariensis.

Hildebrand has shown in the paper referred to under the last species, that this hermaphrodite grass is better adapted for cross-fertilisation than for self-fertilisation. Several plants were raised in the greenhouse close together, and their flowers were mutually intercrossed. Pollen from a single plant growing quite separately was collected and placed on the stigmas of the same plant. The seeds thus produced were self-fertilised, for they were fertilised with pollen from the same plant, but it will have been a mere chance whether with pollen from the same flowers. Both lots of seeds, after germinating on sand, were planted in pairs on the opposite sides of four pots, which were kept in the greenhouse. When the plants were a little over a foot in height they were measured, and the crossed plants averaged 13.38, and the self-fertilised 12.29 inches in height; or as 100 to 92.

When in full flower they were again measured to the extremities of their culms, as shown in Table 6/98.

TABLE 6/98. Phalaris canariensis.

Heights of plants measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 42 2/8 : 41 2/8. Pot 1 : 39 6/8 : 45 4/8.

Pot 2 : 37 : 31 6/8. Pot 2 : 49 4/8 : 37 2/8. Pot 4 : 29 : 42 3/8. Pot 2 : 37 : 34 7/8.

Pot 3 : 37 6/8 : 28. Pot 3 : 35 4/8 : 28. Pot 3 : 43 : 34.

Pot 4 : 40 2/8 : 35 1/8. Pot 4 : 37 : 34 4/8.

Total : 428.00 : 392.63.

The eleven crossed plants now averaged 38.9, and the eleven self-fertilised plants 35.69 inches in height; or as 100 to 92, which is the same ratio as before. Differently to what occurred with the maize, the crossed plants did not flower before the self-fertilised; and though both lots flowered very poorly from having been kept in pots in the greenhouse, yet the self-fertilised plants produced twenty-eight flower-heads, whilst the crossed produced only twenty!

Two long rows of the same seeds were sown out of doors, and care was taken that they were sown in nearly equal number; but a far greater number of the crossed than of the self-fertilised seeds yielded plants. The self-fertilised plants were in consequence not so much crowded as the crossed, and thus had an advantage over them. When in full flower, the twelve tallest plants were carefully selected from both rows and measured, as shown in Table 6/99.

TABLE 6/99. Phalaris canariensis (growing in the open ground).

Heights of plants measured in inches.

Column 1: Crossed Plants, twelve tallest.

Column 2: Self-fertilised Plants, twelve tallest.

34 1/8 : 35 2/8.
35 7/8 : 31 1/8.
36 : 33.
35 5/8 : 32.
35 5/8 : 31 5/8.
36 1/8 : 36.
36 6/8 : 33.
38 6/8 : 32.
36 2/8 : 35 1/8.
35 5/8 : 33 5/8.
34 1/8 : 34 2/8.
34 5/8 : 35.

Total : 429.5 : 402.0.

The twelve crossed plants here average 35.78, and the twelve self-fertilised 33.5 inches in height; or as 100 to 93. In this case the crossed plants flowered rather before the self-fertilised, and thus differed from those growing in the pots.]

CHAPTER VII. A SUMMARY OF THE HEIGHTS AND WEIGHTS OF THE CROSSED AND SELF-FERTILISED PLANTS.

Number of species and plants measured.
Tables given.
Preliminary remarks on the offspring of plants crossed by a fresh stock.
Thirteen cases specially considered.
The effects of crossing a self-fertilised plant either by another
self-fertilised plant or by an intercrossed plant of the old stock.
Summary of the results.
Preliminary remarks on the crossed and self-fertilised plants of the
same stock.
The twenty-six exceptional cases considered, in which the crossed plants
did not exceed greatly in height the self-fertilised.
Most of these cases shown not to be real exceptions to the rule that
cross-fertilisation is beneficial.
Summary of results.
Relative weights of the crossed and self-fertilised plants.

The details which have been given under the head of each species are so numerous and so intricate, that it is necessary to tabulate the results. In Table 7/A, the number of plants of each kind which were raised from a cross between two individuals of the same stock and from self-fertilised seeds, together with their mean or average heights, are given. In the right hand column, the mean height of the crossed to that of the self-fertilised plants, the former being taken as 100, is shown. To make this clear, it may be advisable to give an example. In the first generation of Ipomoea, six plants derived from a cross between two plants were measured, and their mean height is 86.00 inches; six plants derived from flowers on the same parent-plant fertilised with their own pollen were measured, and their mean height is 65.66 inches. From this it follows, as shown in the right hand column, that if the mean height of the crossed plants be taken as 100, that of the self-fertilised plants is 76. The same plan is followed with all the other species.

The crossed and self-fertilised plants were generally grown in pots in competition with one another, and always under as closely similar conditions as could be attained. They were, however, sometimes grown in separate rows in the open ground. With several of the species, the crossed plants were again crossed, and the self-fertilised plants again self-fertilised, and thus successive generations were raised and measured, as may be seen in Table 7/A. Owing to this manner of proceeding, the crossed plants became in the later generations more or less closely inter-related.

In Table 7/B the relative weights of the crossed and self-fertilised plants, after they had flowered and had been cut down, are given in the few cases in which they were ascertained. The results are, I think, more striking and of greater value as evidence of constitutional vigour than those deduced from the relative heights of the plants.

The most important table is Table 7/C, as it includes the relative heights, weights, and fertility of plants raised from parents crossed by a fresh stock (that is, by non-related plants grown under different conditions), or by a distinct sub-variety, in comparison with self-fertilised plants, or in a few cases with plants of the same old stock intercrossed during several generations. The relative fertility of the plants in this and the other tables will be more fully considered in a future chapter.

TABLE 7/A. Relative heights of plants from parents crossed with pollen from other plants of the same stock, and self-fertilised.

Heights of plants measured in inches.

Column 1: Name of Plant.

Column 2: Number of Crossed Plants measured.

Column 3: Average Height of Crossed Plants.

Column 4: Number of Self-fertilised Plants measured.

Column 5: Average Height of Self-fertilised Plants.

Column 6: x, where the ratio of the Average Height of the Crossed to the Self-fertilised Plants is expressed as 100 to x.

Ipomoea purpurea—first generation:
6 : 86.00 : 6 : 65.66 : 76.

Ipomoea purpurea—second generation:
6 : 84.16 : 6 : 66.33 : 79.

Ipomoea purpurea—third generation:
6 : 77.41 : 6 : 52.83 : 68.

Ipomoea purpurea—fourth generation:
7 : 69.78 : 7 : 60.14 : 86.

Ipomoea purpurea—fifth generation:
6 : 82.54 : 6 : 62.33 : 75.

Ipomoea purpurea—sixth generation:
6 : 87.50 : 6 : 63.16 : 72.

Ipomoea purpurea—seventh generation:
9 : 83.94 : 9 : 68.25 : 81.

Ipomoea purpurea—eighth generation:
8 : 113.25 : 8 : 96.65 : 85.

Ipomoea purpurea—ninth generation:
14 : 81.39 : 14 : 64.07 : 79.

Ipomoea purpurea—tenth generation:
5 : 93.70 : 5 : 50.40 : 54.

Ipomoea purpurea—Number and average height of all the plants of the ten
generations:
73 : 85.84 : 73 : 66.02 : 77.

Mimulus luteus—three first generations, before the new and taller
self-fertilised variety appeared:
10 : 8.19 : 10 : 5.29 : 65.

Digitalis purpurea:
16 : 51.33 : 8 : 35.87 : 70.

Calceolaria—(common greenhouse variety):
1 : 19.50 : 1 : 15.00 : 77.

Linaria vulgaris:
3 : 7.08 : 3 : 5.75 : 81.

Verbascum thapsus:
6 : 65.34 : 6 : 56.50 : 86.

Vandellia nummularifolia—crossed and self-fertilised plants, raised
from perfect flowers:
20 : 4.30 : 20 : 4.27 : 99.

Vandellia nummularifolia—crossed and self-fertilised plants, raised
from perfect flowers: second trial, plants crowded:
24 : 3.60 : 24 : 3.38 : 94.

Vandellia nummularifolia—crossed plants raised from perfect flowers,
and self-fertilised plants from cleistogene flowers:
20 : 4.30 : 20 : 4.06 : 94.

Gesneria pendulina:
8 : 32.06 : 8 : 29.14 : 90.

Salvia coccinea:
6 : 27.85 : 6 : 21.16 : 76.

Origanum vulgare:
4 : 20.00 : 4 : 17.12 : 86.

Thunbergia alata:
6 : 60.00 : 6 : 65.00 : 108.

Brassica oleracea:
9 : 41.08 : 9 : 39.00 : 95.

Iberis umbellata—the self-fertilised plants of the third generation:
7 : 19.12 : 7 : 16.39 : 86.

Papaver vagum:
15 : 21.91 : 15 : 19.54 : 89.

Eschscholtzia californica—English stock, first generation:
4 : 29.68 : 4 : 25.56 : 86.

Eschscholtzia californica—English stock, second generation:
11 : 32.47 : 11 : 32.81 : 101.

Eschscholtzia californica—Brazilian stock, first generation:
14 : 44.64 : 14 : 45.12 : 101.

Eschscholtzia californica—Brazilian stock, second generation:
18 : 43.38 : 19 : 50.30 : 116.

Eschscholtzia californica—average height and number of all the plants
of Eschscholtzia:
47 : 40.03 : 48 : 42.72 : 107.

Reseda lutea—grown in pots:
24 : 17.17 : 24 : 14.61 : 85.

Reseda lutea—grown in open ground :
8 : 28.09 : 8 : 23.14 : 82.

Reseda odorata—self-fertilised seeds from a highly self-fertile plant,
grown in pots:
19 : 27.48 : 19 : 22.55 : 82.

Reseda odorata—self-fertilised seeds from a highly self-fertile plant,
grown in open ground:
8 : 25.76 : 8 : 27.09 : 105.

Reseda odorata—self-fertilised seeds from a semi-self-fertile plant,
grown in pots:
20 : 29.98 : 20 : 27.71 : 92.

Reseda odorata—self-fertilised seeds from a semi-self-fertile plant,
grown in open ground:
8 : 25.92 : 8 : 23.54 : 90.

Viola tricolor:
14 : 5.58 : 14 : 2.37 : 42.

Adonis aestivalis:
4 : 14.25 : 4 : 14.31 : 100.

Delphinium consolida:
6 : 14.95 : 6 : 12.50 : 84.

Viscaria oculata:
15 : 34.50 : 15 : 33.55 : 97.

Dianthus caryophyllus—open ground, about :
6?: 28? : 6?: 24? : 86.

Dianthus caryophyllus—second generation, in pots, crowded:
2 : 16.75 : 2 : 9.75 : 58.

Dianthus caryophyllus—third generation, in pots:
8 : 28.39 : 8 : 28.21 : 99.

Dianthus caryophyllus—offspring from plants of the third
self-fertilised generation crossed by intercrossed plants of the third
generation, compared with plants of fourth self-fertilised generation:
15 : 28.00 : 10 : 26.55 : 95.

Dianthus caryophyllus—number and average height of all the plants of
Dianthus:
31 : 27.37 : 26 : 25.18 : 92.

Hibiscus africanus:
4 : 13.25 : 4 : 14.43 : 109.

Pelargonium zonale:
7 : 22.35 : 7 : 16.62 : 74.

Tropaeolum minus:
8 : 58.43 : 8 : 46.00 : 79.

Limnanthes douglasii:
16 : 17.46 : 16 : 13.85 : 79.

Lupinus luteus—second generation:
8 : 30.78 : 8 : 25.21 : 82.

Lupinus pilosus—plants of two generations:
2 : 35.50 : 3 : 30.50 : 86.

Phaseolus multiflorus:
5 : 86.00 : 5 : 82.35 : 96.

Pisum sativum:
4 : 34.62 : 4 : 39.68 : 115.

Sarothamnus scoparius—small seedlings:
6 : 2.91 : 6 : 1.33 : 46.

Sarothamnus scoparius—the three survivors on each side after three
years’ growth:
: 18.91 : : 11.83 : 63.

Ononis minutissima:
2 : 19.81 : 2 : 17.37 : 88.

Clarkia elegans:
4 : 33.50 : 4 : 27.62 : 82.

Bartonia aurea:
8 : 24.62 : 8 : 26.31 : 107.

Passiflora gracilis:
2 : 49.00 : 2 : 51.00 : 104.

Apium petroselinum:
* : : * : : 100.
*not measured.

Scabiosa atro-purpurea:
4 : 17.12 : 4 : 15.37 : 90.

Lactuca sativa—plants of two generations:
7 : 19.43 : 6 : 16.00 : 82.

Specularia speculum:
4 : 19.28 : 4 : 18.93 : 98.

Lobelia ramosa—first generation:
4 : 22.25 : 4 : 18.37 : 82.

Lobelia ramosa—second generation:
3 : 23.33 : 3 : 19.00 : 81.

Lobelia fulgens—first generation:
2 : 34.75 : 2 : 44.25 : 127.

Lobelia fulgens—second generation:
23 : 29.82 : 23 : 27.10 : 91.

Nemophila insignis—half-grown:
12 : 11.10 : 12 : 5.45 : 49.

Nemophila insignis—the same fully-grown:
: 33.28 : : 19.90 : 60.

Borago officinalis:
4 : 20.68 : 4 : 21.18 : 102.

Nolana prostrata:
5 : 12.75 : 5 : 13.40 : 105.

Petunia violacea—first generation:
5 : 30.80 : 5 : 26.00 : 84.

Petunia violacea—second generation:
4 : 40.50 : 6 : 26.25 : 65.

Petunia violacea—third generation:
8 : 40.96 : 8 : 53.87 : 131.

Petunia violacea—fourth generation:
15 : 46.79 : 14 : 32.39 : 69.

Petunia violacea—fourth generation, from a distinct parent:
13 : 44.74 : 13 : 26.87 : 60.

Petunia violacea—fifth generation:
22 : 54.11 : 21 : 33.23 : 61.

Petunia violacea—fifth generation, in open ground:
10 : 38.27 : 10 : 23.31 : 61.

Petunia violacea—Number and average height of all the plants in pots of
Petunia:
67 : 46.53 : 67 : 33.12 : 71.

Nicotiana tabacum—first generation:
4 : 18.50 : 4 : 32.75 : 178.

Nicotiana tabacum—second generation:
9 : 53.84 : 7 : 51.78 : 96.

Nicotiana tabacum—third generation:
7 : 95.25 : 7 : 79.60 : 83.

Nicotiana tabacum—third generation but raised from a distinct plant:
7 : 70.78 : 9 : 71.30 : 101.

Nicotiana tabacum—Number and average height of all the plants of
Nicotiana:
27 : 63.73 : 27 : 61.31 : 96.

Cyclamen persicum:
8 : 9.49 : 8?: 7.50 : 79.

Anagallis collina:
6 : 42.20 : 6 : 33.35 : 69.

Primula sinensis—a dimorphic species:
8 : 9.01 : 8 : 9.03 : 100.

Fagopyrum esculentum—a dimorphic species:
15 : 38.06 : 15 : 26.13 : 69.

Beta vulgaris—in pots:
8 : 34.09 : 8 : 29.81 : 87.

Beta vulgaris—in open ground:
8 : 30.92 : 8 : 30.70 : 99.

Canna warscewiczi—plants of three generations:
34 : 35.98 : 34 : 36.39 : 101.

Zea mays—in pots, whilst young, measured to tips of leaves:
15 : 20.19 : 15 : 17.57 : 87.

Zea mays—when full-grown, after the death of some, measured to tips of
leaves:
: 68.10 : : 62.34 : 91.

Zea mays—when full-grown, after the death of some, measured to tips of
flowers:
: 66.51 : : 61.59 : 93.

Zea mays—grown in open ground, measured to tips of leaves:
10 : 54.00 : 10 : 44.55 : 83.

Zea mays—grown in open ground, measured to tips of flowers:
: 53.96 : : 43.45 : 80.

Phalaris canariensis—in pots.
11 : 38.90 : 11 : 35.69 : 92.

Phalaris canariensis—in open ground:
12 : 35.78 : 12 : 33.50 : 93.

TABLE 7/B.—Relative weights of plants from parents crossed with pollen from distinct plants of the same stock, and self-fertilised.

Column 1: Names of plants.

Column 2: Number of crossed plants.

Column 3: Number of self-fertilised plants.

Column 4: x, where the ratio of the Weight of the Crossed to the Self-fertilised Plants is expressed as 100 to x.

Ipomoea purpurea—plants of the tenth generation:
6 : 6 : 44.

Vandellia nummularifolia—first generation:
41 : 41 : 97.

Brassica oleracea—first generation:
9 : 9 : 37.

Eschscholtzia californica—plants of the second generation:
19 : 19 : 118.

Reseda lutea—first generation, grown in pots:
24 : 24 : 21.

Reseda lutea—first generation, grown in open ground:
8 : 8 : 40.

Reseda odorata—first generation, descended from a highly self-fertile
plant, grown in pots:
19 : 19 : 67.

Reseda odorata—first generation, descended from a semi-self-fertile
plant, grown in pots:
20 : 20 : 99.

Dianthus caryophyllus—plants of the third generation:
8 : 8 : 49.

Petunia violacea—plants of the fifth generation, in pots:
22 : 21 : 22.

Petunia violacea—plants of the fifth generation, in open ground:
10 : 10 : 36.

TABLE 7/C.—Relative heights, weights, and fertility of plants from parents crossed by a fresh stock, and from parents either self-fertilised or intercrossed with plants of the same stock.

Column 1: Names of the plants and nature of the experiments.

Column 2: Number of plants from a cross with a fresh stock.

Column 3: Average height in inches and weight.

Column 4: Number of the plants from self-fertilised or intercrossed parents of the same stock.

Column 5: Average height in inches and weight.

Column 4: x, where the ratio of the Height, Weight and Fertility of the plants from the Cross with a fresh stock is expressed as 100 to x.

Ipomoea purpurea—offspring of plants intercrossed for nine generations
and then crossed by a fresh stock, compared with plants of the tenth
intercrossed generation:
19 : 84.03 : 19 : 65.78 : 78.

Ipomoea purpurea—offspring of plants intercrossed for nine generations
and then crossed by a fresh stock, compared with plants of the tenth
intercrossed generation, in fertility:
.. : .. : .. : .. : 51.

Mimulus luteus—offspring of plants self-fertilised for eight
generations and then crossed by a fresh stock, compared with plants of
the ninth self-fertilised generation:
28 : 21.62 : 19 : 10.44 : 52.

Mimulus luteus—offspring of plants self-fertilised for eight
generations and then crossed by a fresh stock, compared with plants of
the ninth self-fertilised generation, in fertility:
.. : .. : .. : .. : 3.

Mimulus luteus—offspring of plants self-fertilised for eight
generations and then crossed by a fresh stock, compared with the
offspring of a plant self-fertilised for eight generations, and then
intercrossed with another self-fertilised plant of the same generation:
28 : 21.62 : 27 : 12.20 : 56.

Brassica oleracea—offspring of plants self-fertilised for two
generations and then crossed by a fresh stock, compared with plants of
the third self-fertilised generation, by weight:
6 : : 6 : : 22.

Iberis umbellata—offspring from English variety crossed by slightly
different Algerine variety, compared with the self-fertilised offspring
of the English variety:
30 : 17.34 : 29 : 15.51 : 89.

Iberis umbellata—offspring from English variety crossed by slightly
different Algerine variety, compared with the self-fertilised offspring
of the English variety, in fertility:
.. : .. : .. : .. : 75.

Eschscholtzia californica—offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
self-fertilised generation:
19 : 45.92 : 19 : 50.30 : 109.

Eschscholtzia californica—offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
self-fertilised generation, in weight:
.. : .. : .. : .. : 118.

Eschscholtzia californica—offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
intercrossed generation, in height:
19 : 45.92 : 18 : 43.38 : 94.

Eschscholtzia californica—offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
intercrossed generation, in weight:
.. : .. : .. : .. : 100.

Eschscholtzia californica—offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
intercrossed generation, in fertility:
.. : .. : .. : .. : 45.

Dianthus caryophyllus—offspring of plants self-fertilised for three
generations and then crossed by a fresh stock, compared with plants of
the fourth self-fertilised generation:
16 : 32.82 : 10 : 26.55 : 81.

Dianthus caryophyllus—offspring of plants self-fertilised for three
generations and then crossed by a fresh stock, compared with the
offspring of plants self-fertilised for three generations and then
crossed by plants of the third intercrossed generation:
16 : 32.82 : 15 : 28.00 : 85.

Pisum sativum—offspring from a cross between two closely allied
varieties, compared with the self-fertilised offspring of one of the
varieties, or with intercrossed plants of the same stock:
? : : ? : : 60 to 75.

Lathyrus odoratus—offspring from two varieties, differing only in
colour of their flowers, compared with the self-fertilised offspring of
one of the varieties: in first generation:
2 : 79.25 : 2 : 63.75 : 80.

Lathyrus odoratus—offspring from two varieties, differing only in
colour of their flowers, compared with the self-fertilised offspring of
one of the varieties: in second generation:
6 : 62.91 : 6 : 55.31 : 88.

Petunia violacea—offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth self-fertilised generation, in height:
21 : 50.05 : 21 : 33.23 : 66.

Petunia violacea—offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth self-fertilised generation, grown in open ground, in height:
10 : 36.67 : 10 : 23.31 : 63.

Petunia violacea—offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, in height:
21 : 50.05 : 22 : 54.11 : 108.

Petunia violacea—offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, in weight:
.. : .. : .. : .. : 101.

Petunia violacea—offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, grown in open ground, in height:
10 : 36.67 : 10 : 38.27 : 104.

Nicotiana tabacum—offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown not much
crowded in pots, in height:
26 : 63.29 : 26 : 41.67 : 66.

Nicotiana tabacum—offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown much crowded
in pots, in height:
12 : 31.53 : 12 : 17.21 : 54.

Nicotiana tabacum—offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown much crowded
in pots, in weight:
.. : .. : .. : .. : 37.

Nicotiana tabacum—offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown in open
ground, in height:
20 : 48.74 : 20 : 35.20 : 72.

Anagallis collina—offspring from a red variety crossed by a blue
variety, compared with the self-fertilised offspring of the red variety:
3 : 27.62 : 3 : 18.21 : 66.

Anagallis collina—offspring from a red variety crossed by a blue
variety, compared with the self-fertilised offspring of the red variety,
in fertility:
.. : .. : .. : .. : 6.

Primula veris—offspring from long-styled plants of the third
illegitimate generation, crossed by a fresh stock, compared with plants
of the fourth illegitimate and self-fertilised generation:
8 : 7.03 : 8 : 3.21 : 46.

Primula veris—(equal-styled, red-flowered variety)—offspring from
plants self-fertilised for two generations and then crossed by a
different variety, compared with plants of the third self-fertilised
generation:
3 : 8.66 : 3 : 7.33 : 85.

In these three tables the measurements of fifty-seven species, belonging to fifty-two genera and to thirty great natural families, are given. The species are natives of various parts of the world. The number of crossed plants, including those derived from a cross between plants of the same stock and of two different stocks, amounts to 1,101; and the number of self-fertilised plants (including a few in Table 7/C derived from a cross between plants of the same old stock) is 1,076. Their growth was observed from the germination of the seeds to maturity; and most of them were measured twice and some thrice. The various precautions taken to prevent either lot being unduly favoured, have been described in the introductory chapter. Bearing all these circumstances in mind, it may be admitted that we have a fair basis for judging of the comparative effects of cross-fertilisation and of self-fertilisation on the growth of the offspring.

It will be the most convenient plan first to consider the results given in Table 7/C, as an opportunity will thus be afforded of incidentally discussing some important points. If the reader will look down the right hand column of this table, he will see at a glance what an extraordinary advantage in height, weight, and fertility the plants derived from a cross with a fresh stock or with another sub-variety have over the self-fertilised plants, as well as over the intercrossed plants of the same old stock. There are only two exceptions to this rule, and these are hardly real ones. In the case of Eschscholtzia, the advantage is confined to fertility. In that of Petunia, though the plants derived from a cross with a fresh stock had an immense superiority in height, weight, and fertility over the self-fertilised plants, they were conquered by the intercrossed plants of the same old stock in height and weight, but not in fertility. It has, however, been shown that the superiority of these intercrossed plants in height and weight was in all probability not real; for if the two sets had been allowed to grow for another month, it is almost certain that those from a cross with the fresh stock would have been victorious in every way over the intercrossed plants.

Before we consider in detail the several cases given in Table 7/C, some preliminary remarks must be made. There is the clearest evidence, as we shall presently see, that the advantage of a cross depends wholly on the plants differing somewhat in constitution; and that the disadvantages of self-fertilisation depend on the two parents, which are combined in the same hermaphrodite flower, having a closely similar constitution. A certain amount of differentiation in the sexual elements seems indispensable for the full fertility of the parents, and for the full vigour of the offspring. All the individuals of the same species, even those produced in a state of nature, differ somewhat, though often very slightly, from one another in external characters and probably in constitution. This obviously holds good between the varieties of the same species, as far as external characters are concerned; and much evidence could be advanced with respect to their generally differing somewhat in constitution. There can hardly be a doubt that the differences of all kinds between the individuals and varieties of the same species depend largely, and as I believe exclusively, on their progenitors having been subjected to different conditions; though the conditions to which the individuals of the same species are exposed in a state of nature often falsely appear to us the same. For instance, the individuals growing together are necessarily exposed to the same climate, and they seem to us at first sight to be subjected to identically the same conditions; but this can hardly be the case, except under the unusual contingency of each individual being surrounded by other kinds of plants in exactly the same proportional numbers. For the surrounding plants absorb different amounts of various substances from the soil, and thus greatly affect the nourishment and even the life of the individuals of any particular species. These will also be shaded and otherwise affected by the nature of the surrounding plants. Moreover, seeds often lie dormant in the ground, and those which germinate during any one year will often have been matured during very different seasons. Seeds are widely dispersed by various means, and some will occasionally be brought from distant stations, where their parents have grown under somewhat different conditions, and the plants produced from such seeds will intercross with the old residents, thus mingling their constitutional peculiarities in all sorts of proportions.

Plants when first subjected to culture, even in their native country, cannot fail to be exposed to greatly changed conditions of life, more especially from growing in cleared ground, and from not having to compete with many or any surrounding plants. They are thus enabled to absorb whatever they require which the soil may contain. Fresh seeds are often brought from distant gardens, where the parent-plants have been subjected to different conditions. Cultivated plants like those in a state of nature frequently intercross, and will thus mingle their constitutional peculiarities. On the other hand, as long as the individuals of any species are cultivated in the same garden, they will apparently be subjected to more uniform conditions than plants in a state of nature, as the individuals have not to compete with various surrounding species. The seeds sown at the same time in a garden have generally been matured during the same season and in the same place; and in this respect they differ much from the seeds sown by the hand of nature. Some exotic plants are not frequented by the native insects in their new home, and therefore are not intercrossed; and this appears to be a highly important factor in the individuals acquiring uniformity of constitution.

In my experiments the greatest care was taken that in each generation all the crossed and self-fertilised plants should be subjected to the same conditions. Not that the conditions were absolutely the same, for the more vigorous individuals will have robbed the weaker ones of nutriment, and likewise of water when the soil in the pots was becoming dry; and both lots at one end of the pot will have received a little more light than those at the other end. In the successive generations, the plants were subjected to somewhat different conditions, for the seasons necessarily varied, and they were sometimes raised at different periods of the year. But as they were all kept under glass, they were exposed to far less abrupt and great changes of temperature and moisture than are plants growing out of doors. With respect to the intercrossed plants, their first parents, which were not related, would almost certainly have differed somewhat in constitution; and such constitutional peculiarities would be variously mingled in each succeeding intercrossed generation, being sometimes augmented, but more commonly neutralised in a greater or less degree, and sometimes revived through reversion; just as we know to be the case with the external characters of crossed species and varieties. With the plants which were self-fertilised during the successive generations, this latter important source of some diversity of constitution will have been wholly eliminated; and the sexual elements produced by the same flower must have been developed under as nearly the same conditions as it is possible to conceive.

In Table 7/C the crossed plants are the offspring of a cross with a fresh stock, or with a distinct variety; and they were put into competition either with self-fertilised plants, or with intercrossed plants of the same old stock. By the term fresh stock I mean a non-related plant, the progenitors of which have been raised during some generations in another garden, and have consequently been exposed to somewhat different conditions. In the case of Nicotiana, Iberis, the red variety of Primula, the common Pea, and perhaps Anagallis, the plants which were crossed may be ranked as distinct varieties or sub-varieties of the same species; but with Ipomoea, Mimulus, Dianthus, and Petunia, the plants which were crossed differed exclusively in the tint of their flowers; and as a large proportion of the plants raised from the same lot of purchased seeds thus varied, the differences may be estimated as merely individual. Having made these preliminary remarks, we will now consider in detail the several cases given in Table 7/C, and they are well worthy of full consideration.

1. Ipomoea purpurea.

Plants growing in the same pots, and subjected in each generation to the same conditions, were intercrossed for nine consecutive generations. These intercrossed plants thus became in the later generations more or less closely inter-related. Flowers on the plants of the ninth intercrossed generation were fertilised with pollen taken from a fresh stock, and seedlings thus raised. Other flowers on the same intercrossed plants were fertilised with pollen from another intercrossed plant, producing seedlings of the tenth intercrossed generation. These two sets of seedlings were grown in competition with one another, and differed greatly in height and fertility. For the offspring from the cross with a fresh stock exceeded in height the intercrossed plants in the ratio of 100 to 78; and this is nearly the same excess which the intercrossed had over the self-fertilised plants in all ten generations taken together, namely, as 100 to 77. The plants raised from the cross with a fresh stock were also greatly superior in fertility to the intercrossed, namely, in the ratio of 100 to 51, as judged by the relative weight of the seed-capsules produced by an equal number of plants of the two sets, both having been left to be naturally fertilised. It should be especially observed that none of the plants of either lot were the product of self-fertilisation. On the contrary, the intercrossed plants had certainly been crossed for the last ten generations, and probably, during all previous generations, as we may infer from the structure of the flowers and from the frequency of the visits of humble-bees. And so it will have been with the parent-plants of the fresh stock. The whole great difference in height and fertility between the two lots must be attributed to the one being the product of a cross with pollen from a fresh stock, and the other of a cross between plants of the same old stock.

This species offers another interesting case. In the five first generations in which intercrossed and self-fertilised plants were put into competition with one another, every single intercrossed plant beat its self-fertilised antagonist, except in one instance, in which they were equal in height. But in the sixth generation a plant appeared, named by me the Hero, remarkable for its tallness and increased self-fertility, and which transmitted its characters to the next three generations. The children of Hero were again self-fertilised, forming the eighth self-fertilised generation, and were likewise intercrossed one with another; but this cross between plants which had been subjected to the same conditions and had been self-fertilised during the seven previous generations, did not effect the least good; for the intercrossed grandchildren were actually shorter than the self-fertilised grandchildren, in the ratio of 100 to 107. We here see that the mere act of crossing two distinct plants does not by itself benefit the offspring. This case is almost the converse of that in the last paragraph, on which the offspring profited so greatly by a cross with a fresh stock. A similar trial was made with the descendants of Hero in the following generation, and with the same result. But the trial cannot be fully trusted, owing to the extremely unhealthy condition of the plants. Subject to this same serious cause of doubt, even a cross with a fresh stock did not benefit the great-grandchildren of Hero; and if this were really the case, it is the greatest anomaly observed by me in all my experiments.

2. Mimulus luteus.

During the three first generations the intercrossed plants taken together exceeded in height the self-fertilised taken together, in the ratio of 100 to 65, and in fertility in a still higher degree. In the fourth generation a new variety, which grew taller and had whiter and larger flowers than the old varieties, began to prevail, especially amongst the self-fertilised plants. This variety transmitted its characters with remarkable fidelity, so that all the plants in the later self-fertilised generations belonged to it. These consequently exceeded the intercrossed plants considerably in height. Thus in the seventh generation the intercrossed plants were to the self-fertilised in height as 100 to 137. It is a more remarkable fact that the self-fertilised plants of the sixth generation had become much more fertile than the intercrossed plants, judging by the number of capsules spontaneously produced, in the ratio of 147 to 100. This variety, which as we have seen appeared amongst the plants of the fourth self-fertilised generation, resembles in almost all its constitutional peculiarities the variety called Hero which appeared in the sixth self-fertilised generation of Ipomoea. No other such case, with the partial exception of that of Nicotiana, occurred in my experiments, carried on during eleven years.

Two plants of this variety of Mimulus, belonging to the sixth self-fertilised generation, and growing in separate pots, were intercrossed; and some flowers on the same plants were again self-fertilised. From the seeds thus obtained, plants derived from a cross between the self-fertilised plants, and others of the seventh self-fertilised generation, were raised. But this cross did not do the least good, the intercrossed plants being inferior in height to the self-fertilised, in the ratio of 100 to 110. This case is exactly parallel with that given under Ipomoea, of the grandchildren of Hero, and apparently of its great-grandchildren; for the seedlings raised by intercrossing these plants were not in any way superior to those of the corresponding generation raised from the self-fertilised flowers. Therefore in these several cases the crossing of plants, which had been self-fertilised for several generations and which had been cultivated all the time under as nearly as possible the same conditions, was not in the least beneficial.

Another experiment was now tried. Firstly, plants of the eighth self-fertilised generation were again self-fertilised, producing plants of the ninth self-fertilised generation. Secondly, two of the plants of the eighth self-fertilised generation were intercrossed one with another, as in the experiment above referred to; but this was now effected on plants which had been subjected to two additional generations of self-fertilisation. Thirdly, the same plants of the eighth self-fertilised generation were crossed with pollen from plants of a fresh stock brought from a distant garden. Numerous plants were raised from these three sets of seeds, and grown in competition with one another. The plants derived from a cross between the self-fertilised plants exceeded in height by a little the self-fertilised, namely, as 100 to 92; and in fertility in a greater degree, namely, as 100 to 73. I do not know whether this difference in the result, compared with that in the previous case, can be accounted for by the increased deterioration of the self-fertilised plants from two additional generations of self-fertilisation, and the consequent advantage of any cross whatever, along merely between the self-fertilised plants. But however this may be, the effects of crossing the self-fertilised plants of the eighth generation with a fresh stock were extremely striking; for the seedlings thus raised were to the self-fertilised of the ninth generation as 100 to 52 in height, and as 100 to 3 in fertility! They were also to the intercrossed plants (derived from crossing two of the self-fertilised plants of the eighth generation) in height as 100 to 56, and in fertility as 100 to 4. Better evidence could hardly be desired of the potent influence of a cross with a fresh stock on plants which had been self-fertilised for eight generations, and had been cultivated all the time under nearly uniform conditions, in comparison with plants self-fertilised for nine generations continuously, or then once intercrossed, namely in the last generation.

3. Brassica oleracea.

Some flowers on cabbage plants of the second self-fertilised generation were crossed with pollen from a plant of the same variety brought from a distant garden, and other flowers were again self-fertilised. Plants derived from a cross with a fresh stock and plants of the third self-fertilised generation were thus raised. The former were to the self-fertilised in weight as 100 to 22; and this enormous difference must be attributed in part to the beneficial effects of a cross with a fresh stock, and in part to the deteriorating effects of self-fertilisation continued during three generations.

4. Iberis umbellata.

Seedlings from a crimson English variety crossed by a pale-coloured variety which had been grown for some generations in Algiers, were to the self-fertilised seedlings from the crimson variety in height as 100 to 89, and as 100 to 75 in fertility. I am surprised that this cross with another variety did not produce a still more strongly marked beneficial effect; for some intercrossed plants of the crimson English variety, put into competition with plants of the same variety self-fertilised during three generations, were in height as 100 to 86, and in fertility as 100 to 75. The slightly greater difference in height in this latter case, may possibly be attributed to the deteriorating effects of self-fertilisation carried on for two additional generations.

5. Eschscholtzia californica.

This plant offers an almost unique case, inasmuch as the good effects of a cross are confined to the reproductive system. Intercrossed and self-fertilised plants of the English stock did not differ in height (nor in weight, as far as was ascertained) in any constant manner; the self-fertilised plants usually having the advantage. So it was with the offspring of plants of the Brazilian stock, tried in the same manner. The parent-plants, however, of the English stock produced many more seeds when fertilised with pollen from another plant than when self-fertilised; and in Brazil the parent-plants were absolutely sterile unless they were fertilised with pollen from another plant. Intercrossed seedlings, raised in England from the Brazilian stock, compared with self-fertilised seedlings of the corresponding second generation, yielded seeds in number as 100 to 89; both lots of plants being left freely exposed to the visits of insects. If we now turn to the effects of crossing plants of the Brazilian stock with pollen from the English stock,—so that plants which had been long exposed to very different conditions were intercrossed,—we find that the offspring were, as before, inferior in height and weight to the plants of the Brazilian stock after two generations of self-fertilisation, but were superior to them in the most marked manner in the number of seeds produced, namely, as 100 to 40; both lots of plants being left freely exposed to the visits of insects.

In the case of Ipomoea, we have seen that the plants derived from a cross with a fresh stock were superior in height as 100 to 78, and in fertility as 100 to 51, to the plants of the old stock, although these had been intercrossed during the last ten generations. With Eschscholtzia we have a nearly parallel case, but only as far as fertility is concerned, for the plants derived from a cross with a fresh stock were superior in fertility in the ratio of 100 to 45 to the Brazilian plants, which had been artificially intercrossed in England for the two last generations, and which must have been naturally intercrossed by insects during all previous generations in Brazil, where otherwise they are quite sterile.

6. Dianthus caryophyllus.

Plants self-fertilised for three generations were crossed with pollen from a fresh stock, and their offspring were grown in competition with plants of the fourth self-fertilised generation. The crossed plants thus obtained were to the self-fertilised in height as 100 to 81, and in fertility (both lots being left to be naturally fertilised by insects) as 100 to 33.

These same crossed plants were also to the offspring from the plants of the third generation crossed by the intercrossed plants of the corresponding generation, in height as 100 to 85, and in fertility as 100 to 45.

We thus see what a great advantage the offspring from a cross with a fresh stock had, not only over the self-fertilised plants of the fourth generation, but over the offspring from the self-fertilised plants of the third generation, when crossed by the intercrossed plants of the old stock.

7. Pisum sativum.

It has been shown under the head of this species, that the several varieties in this country almost invariably fertilise themselves, owing to insects rarely visiting the flowers; and as the plants have been long cultivated under nearly similar conditions, we can understand why a cross between two individuals of the same variety does not do the least good to the offspring either in height or fertility. This case is almost exactly parallel with that of Mimulus, or that of the Ipomoea named Hero; for in these two instances, crossing plants which had been self-fertilised for seven generations did not at all benefit the offspring. On the other hand, a cross between two varieties of the pea causes a marked superiority in the growth and vigour of the offspring, over the self-fertilised plants of the same varieties, as shown by two excellent observers. From my own observations (not made with great care) the offspring from crossed varieties were to self-fertilised plants in height, in one case as 100 to about 75, and in a second case as 100 to 60.

8. Lathyrus odoratus.

The sweet-pea is in the same state in regard to self-fertilisation as the common pea; and we have seen that seedlings from a cross between two varieties, which differed in no respect except in the colour of their flowers, were to the self-fertilised seedlings from the same mother-plant in height as 100 to 80; and in the second generation as 100 to 88. Unfortunately I did not ascertain whether crossing two plants of the same variety failed to produce any beneficial effect, but I venture to predict such would be the result.

9. Petunia violacea.

The intercrossed plants of the same stock in four out of the five successive generations plainly exceeded in height the self-fertilised plants. The latter in the fourth generation were crossed by a fresh stock, and the seedlings thus obtained were put into competition with the self-fertilised plants of the fifth generation. The crossed plants exceeded the self-fertilised in height in the ratio of 100 to 66, and in weight as 100 to 23; but this difference, though so great, is not much greater than that between the intercrossed plants of the same stock in comparison with the self-fertilised plants of the corresponding generation. This case, therefore, seems at first sight opposed to the rule that a cross with a fresh stock is much more beneficial than a cross between individuals of the same stock. But as with Eschscholtzia, the reproductive system was here chiefly benefited; for the plants raised from the cross with the fresh stock were to the self-fertilised plants in fertility, both lots being naturally fertilised, as 100 to 46, whereas the intercrossed plants of the same stock were to the self-fertilised plants of the corresponding fifth generation in fertility only as 100 to 86.

Although at the time of measurement the plants raised from the cross with the fresh stock did not exceed in height or weight the intercrossed plants of the old stock (owing to the growth of the former not having been completed, as explained under the head of this species), yet they exceeded the intercrossed plants in fertility in the ratio of 100 to 54. This fact is interesting, as it shows that plants self-fertilised for four generations and then crossed by a fresh stock, yielded seedlings which were nearly twice as fertile as those from plants of the same stock which had been intercrossed for the five previous generations. We here see, as with Eschscholtzia and Dianthus, that the mere act of crossing, independently of the state of the crossed plants, has little efficacy in giving increased fertility to the offspring. The same conclusion holds good, as we have already seen, in the analogous cases of Ipomoea, Mimulus, and Dianthus, with respect to height.

10. Nicotiana tabacum.

My plants were remarkably self-fertile, and the capsules from the self-fertilised flowers apparently yielded more seeds than those which were cross-fertilised. No insects were seen to visit the flowers in the hothouse, and I suspect that the stock on which I experimented had been raised under glass, and had been self-fertilised during several previous generations; if so, we can understand why, in the course of three generations, the crossed seedlings of the same stock did not uniformly exceed in height the self-fertilised seedlings. But the case is complicated by individual plants having different constitutions, so that some of the crossed and self-fertilised seedlings raised at the same time from the same parents behaved differently. However this may be, plants raised from self-fertilised plants of the third generation crossed by a slightly different sub-variety, exceeded greatly in height and weight the self-fertilised plants of the fourth generation; and the trial was made on a large scale. They exceeded them in height when grown in pots, and not much crowded, in the ratio of 100 to 66; and when much crowded, as 100 to 54. These crossed plants, when thus subjected to severe competition, also exceeded the self-fertilised in weight in the ratio of 100 to 37. So it was, but in a less degree (as may be seen in Table 7/C), when the two lots were grown out of doors and not subjected to any mutual competition. Nevertheless, strange as is the fact, the flowers on the mother-plants of the third self-fertilised generation did not yield more seed when they were crossed with pollen from plants of the fresh stock than when they were self-fertilised.

11. Anagallis collina.

Plants raised from a red variety crossed by another plant of the same variety were in height to the self-fertilised plants from the red variety as 100 to 73. When the flowers on the red variety were fertilised with pollen from a closely similar blue-flowered variety, they yielded double the number of seeds to what they did when crossed by pollen from another individual of the same red variety, and the seeds were much finer. The plants raised from this cross between the two varieties were to the self-fertilised seedlings from the red variety, in height as 100 to 66, and in fertility as 100 to 6.

12. Primula veris.

Some flowers on long-styled plants of the third illegitimate generation were legitimately crossed with pollen from a fresh stock, and others were fertilised with their own pollen. From the seeds thus produced crossed plants, and self-fertilised plants of the fourth illegitimate generation, were raised. The former were to the latter in height as 100 to 46, and in fertility during one year as 100 to 5, and as 100 to 3.5 during the next year. In this case, however, we have no means of distinguishing between the evil effects of illegitimate fertilisation continued during four generations (that is, by pollen of the same form, but taken from a distinct plant) and strict self-fertilisation. But it is probable that these two processes do not differ so essentially as at first appears to be the case. In the following experiment any doubt arising from illegitimate fertilisation was completely eliminated.

13. Primula veris. (Equal-styled, red-flowered variety.)

Flowers on plants of the second self-fertilised generation were crossed with pollen from a distinct variety or fresh stock, and others were again self-fertilised. Crossed plants and plants of the third self-fertilised generation, all of legitimate origin, were thus raised; and the former was to the latter in height as 100 to 85, and in fertility (as judged by the number of capsules produced, together with the average number of seeds) as 100 to 11.