Plant III.
August 20. Thirteen flowers marked to see if autogamy takes place.
August 22. All flowers still on the plant.
August 24. All but two flowers had fallen off. One of these seemed to be developing; the other looked wilted.
August 26. One pod was thriving; the other had wilted and fallen off.
September 13. One pod fully developed.
From the structure of the flowers it would seem that self-pollination would be impossible. When the flower is open, the stigma has never been observed to be in contact with the terminal portion of the large stamen. The stamens do not dehisce until after the flower has opened, nor does the stigma come in contact with the tip of the anther in the bud; thus, clistogamy would be out of the question. It appears from the results obtained from plant III that spontaneous self-pollination is possible. Of course, however, the positive result in this one case should by no means be taken as conclusive evidence of self-pollination. At the present, the most logical explanation to be suggested seems to be that, when the flowers partially close at night, the tips of the pistil and the large stamen are brought into contact. This might occasionally occur, but it is by no means always the case. At the time of the writing of this paper, material for the determination of this point is not available, but two or three flowers examined at night during the summer, before the results of the above experiments had suggested the importance of a careful examination of a large series of material, did not show the stamen and pistil in contact. Of course, note will be taken of the fact that in only one out of thirteen flowers on the plant did spontaneous pollination take place. Another suggestion might be that, approaching so near as they do to each other, a puff of pollen might be thrown from the large stamen and fall upon the pistil when the plant is shaken.
In plants I and II, it will be seen that, in the first case, three fully developed seed pods were obtained from twelve flowers the stigmas of which were supplied with pollen from the large stamen of the same flower. In the second case, one fully developed seed pod was obtained from four pollinated flowers—just twenty-five per cent. in each case.
In the cases in which cross-pollination was effected between right- and left-handed flowers opening simultaneously on the same raceme, we find that, in the first, one pod of the two was only half developed at the end of twenty days. Since the pods are normally fully developed in somewhat less than this length of time, and this undeveloped pod appears somewhat dried, its development seems doubtful. In the second case, one pair of seed pods out of seven pairs of flowers crossed were fully developed, and one seed pod from each of two other pairs were fully and normally developed, making four out of fourteen flowers which yielded seed pods—28.5 per cent.
Professor Todd observed only a small humblebee visiting the flowers of this plant. Owing, probably, to more favorable opportunities for observation, the writers have been able to secure other insects collecting pollen.
The following is a list of the species:
Agapostemon texanus Cress. Two specimens collected August 5, at two p. m. The insects were collecting pollen from the small stamens, to which they clung while they forced the pollen out by pinching the anthers between their fore legs. Pollen was stored on the hind legs. The insect was not seen to come in contact with the tip of the large stamen or the stigma.
Apis mellifica Linn. Taken at two p. m., August 5. They sometimes came in contact with large stamen and pistil, but more often did not touch them at all. Occasionally both stamen and pistil would come in contact with the same side of the insect’s body. Short stamens were sometimes approached from above, the large stamen and pistil remaining untouched.
Anglochora pura Say. Taken at 10:30 a. m., August 6. Obtained pollen from the large stamen by alighting on it, crawling to the tips, and collecting it from the terminal pores.
Halictus sp. A smaller insect than the preceding one, but obtained pollen in the same manner.[J]
No humblebees were taken around Lawrence, although many were noticed working on the plants; consequently the names of the species noticed cannot be given. In St. Joseph, Mo., there were taken at three p. m., when bees were not generally seen working on the plant:
Bombus virginicus. One specimen.
Bombus pennsylvanicus. One specimen.
An examination of fifty flowers taken at this time showed from the dented condition of the small stamens that they had all been visited.
Between eight and nine a. m., September 3, when bees were numerous, there were taken:
Bombus virginicus. Two specimens.
Bombus pennsylvanicus. Twelve specimens.
Bombus scutellaris. One specimen.
The writers found that the humblebees were the principal agents effecting cross-pollination. It was observed that the bee in visiting the flower allowed itself to rest on the tips of the extending stamen and pistil, which, being of the same length, came in contact with both sides of the body just in front of the hind legs, these being left perfectly free. The weight of the bee springs down both stamen and pistil.
Professor Todd’s theory in regard to the pollination of this plant is as follows: “The weight of the bee so springs down the flower, that it is quite difficult, on account of the large, flexible corolla, to see just what is done, but repeated observations led me, quite satisfactorily, to this conclusion. The bee seeks the pollen—for the flowers have neither nectar nor odor—and this she uniformly gets from the four shorter stamens; never, so far as I could determine, from the larger one. This she does by seizing each one, near its base, between her mandibles, and with a sort of milking motion crowds the pollen out of the terminal pores; meanwhile, by the movements of her feet, the larger stamen is repeatedly sprung backwards, and as often throws a cloud of pollen on one side of her body; this in a right-handed flower. When she passes to a left-handed flower, which, as was explained above, is very likely not to be on the same plant, the pollen is carried directly to the pistil of that flower, and so on. We have here, therefore, a novel apparatus for cross-fertilization, quite distinct from those that have been most commonly noticed.”
A considerable quantity of pollen may be thrown from the terminal pores of the large stamen upon tapping it. It thus seems quite possible that some pollen is thrown upon the side of the insect, as described by Professor Todd. All the meaning of Mr. Meehan’s[K] statement is not clear to the writers, but he says, in speaking of Professor Todd’s results: “In regard to the manner in which the pollen is extracted, he found that ‘this she does by seizing each anther near its base between her mandibles, and, with a sort of milking motion, crowds the pollen out of the terminal pores.’ If this were the general way, there would be no necessity for any pollen being ejected from the long stamens, for the stigma would surely receive some during the ‘milking’ process; and the pore at the apex in the long anther is beyond the line of the stigma, so that on ejection from the pore the pollen would go still farther beyond.”
It seems that this statement is of considerable importance for S. rostratum as well as for C. marilandica. Professor Todd very evidently overlooked the fact that, in securing the pollen from the small stamens and transferring it to the hind legs, the sides of the insect are sure to be well dusted with pollen from these stamens. In the case of Apis mellifica, as noted above, there is no certainty that in visiting the flower the same side will be turned toward the stamen or pistil. Even in the case of large insects, such as Bombus, it would seem that the probability that the stigma will be supplied with pollen from the large stamen exclusively is very small. It seems improbable that S. rostratum should depend exclusively upon such an uncertain method of pollination as the projection, by the jarring of a stamen, of a puff of pollen upon the side of an insect, and the subsequent transfer of this pollen to the stigma of a flower of a different type. Of course, it is not improbable that a part of the pollen is furnished by the large stamen, as suggested by Professor Todd, but that fertilization should be effected exclusively by this means seems highly improbable.
The pollen from the large stamen has been shown to be fertile in a certain number of cases, but unfortunately opportunity was not offered for experiments on the fertility of pollen from the small stamens. A rather hasty microscopic examination of fresh, unstained pollen from the large and small stamens reveals no very striking difference in form.
In C. marilandica, Meehan[L] found that the large, strong stamens on each side of the pistil served only as a platform upon which the insect could rest while procuring the pollen from the small stamens. He found that the lower stamens, while filled with pollen, did not dehisce of their own account, nor were they opened by the insect.[M]
The lower stamens and the pistil of the Solanum under consideration serve the purpose of a platform when the flowers are visited by the larger bees. It seems to the writers that this is not improbably the function of the greatest importance of the observed arrangements of the stamen and pistil in S. rostratum. In C. marilandica, the pollen for fertilization, as well as for the attraction of the insect visitor, is furnished by the small stamens, while the pollen produced by the large stamens appears to have no function.[N] The condition is not so specialized in the species of Solanum under consideration. Here the pollen produced by the small anthers serves for the attraction of insects and, as it seems to the writers, for fertilization, while the large stamen, in connection with the pistil, serves as a support for the visiting insect, and possibly furnishes some pollen for cross-fertilization.[O]
In reference to the relative amount of pollen produced by a large and small stamen, Halstead has given a note, in his paper in the Botanical Gazette.[P] The material in the hands of the writers at the time of the writing of this paper is not suitable for a verification of Mr. Halstead’s results; consequently they are simply quoted on his authority. Even if the amount of pollen produced by the large anther is no greater than that produced by one of the smaller, it is still very considerable, as may be readily seen by tapping it out on a glass slip. He says:
“The single large stamen of Solanum rostratum, with its beak-like appearance, is a giant among its fellows, but does not exceed them in the production of pollen, for, while three or four times larger than the others, its thecæ are reduced to narrow, curved lines of mother-cells. The ordinary stamens, on the other hand, possess unusually large cavities in which the pollen is borne. The giant stamen, in cross-section, is shown at a, in fig. 3, while a similar section of an ordinary stamen is shown at b. The almost infertile condition of the large stamen reminds one of the structure of the stamens of the cultivated potatoes. In these, while large and plump, there is almost no pollen-bearing layer, and usually no apical pore opens for the discharge of pollen.”
In C. marilandica, as Meehan has shown, autogamy is impossible, while in S. rostratum autogamy may possibly sometimes take place.
The bee visits the flower for pollen; contrary, however, to the statement of Professor Todd, that “the flowers have neither nectar nor odor,” the writers observed that, especially in the early morning, the odor was decidedly pronounced. It was observed that the bee collected no pollen from the large stamen, but took it regularly from the four smaller. This it did by grasping the anthers, one at a time, near the base, and forcing the pollen out through the terminal pores, by pinching it throughout the length between its mandibles. An exception to this in the case of Agapostemon texanus Cress, is already noted in the list of species. It will be remarked that our observations on this point correspond in general to those of Professor Todd.
Of course the statement of Professor Todd, that the next flower of the opposite type which is visited by the bee is very apt to be on another plant, loses entirely its significance, since it has been shown that the flowers on a branch are not at all likely to be all right- or left-handed. In visiting the flowers, the humblebees, as a general rule, simply pass to the flower most conveniently at hand, and this flower is very apt to be on the same plant, especially where the plants are at all large. The humblebees especially work vigorously in the early morning. In a patch of S. rostratum examined between eight and nine o’clock, in St. Joseph, Mo., nearly all the flowers had already been visited. At this time fifteen specimens of humblebees were taken. A great many flowers would be visited by the bee before it found one which had not already been despoiled of its pollen. In visiting such flowers, the bee would alight for a moment on the pistil and large stamens, as described above, and then pass on to the next flower when it had ascertained that there was no pollen present. In this way over twenty flowers may be visited in a minute. It will be seen that, when the bees are at all numerous and as well dusted with pollen as they usually are, the pistil is almost certain to receive pollen, and fertilization to be effected, especially if the pollen from the small stamens is functional.
Among other insects found visiting the plant, the honey-bee was most frequent.
As will be noticed from our list, some insects visit the plants without effecting cross-pollination. Those insects which obtain pollen in an illegitimate manner do not secure it from the small stamens exclusively, but almost invariably visit the large stamen as well.
The adaptation of the plant to propagation by the production of seeds is of considerable significance.[Q]
A normal plant will produce in the neighborhood of 7000 seeds. In making observations on this point, it was found from five pods examined there was an average of fifty-six seeds.
| Pod | 1 | contained | 66 | seeds. |
| " | 2 | " | 53 | " |
| " | 3 | " | 51 | " |
| " | 4 | " | 53 | " |
| " | 5 | " | 58 | " |
| 281 | seeds; av., 56. | |||
Pods 4 and 5 were from the same plant but separate racemes; the others were from different plants. In determining the average number of seeds produced by the plant, five plants growing normally and in different localities were observed, with the following results:
| Plant | 1 | 192 | pods. |
| " | 2 | 50 | " |
| " | 3 | 66 | " |
| " | 4 | 113 | " |
| " | 5 | 210 | " |
Taking the average of fifty-six seeds per pod obtained above, we see that the plant producing 122.5 pods, the average from the preceding table, would produce about 7000 seeds.
One plant was observed upon which occurred fifty-five to sixty racemes. Allowing the low average of six pods to the raceme, the plant will produce in the neighborhood of 20,000 seeds. Occasionally a very large plant is observed which produces as many as 125 racemes. Allowing the same low average of six pods to the raceme, it will be seen that on a plant of this size there will be produced in the neighborhood of 40,000 seeds.
Only a very small proportion of the ovaries fail to develop. Out of the forty-one racemes observed in five plants, taken at random in different localities, results were obtained as follows:
| Plant | 1, | 5 | racemes | 53 | pods, | 4 | failed. | |
| " | 2, | 5 | " | 42 | " | 3 | " | |
| " | 3, | 9 | " | 55 | " | 5 | " | |
| " | 4, | 11 | " | 91 | " | 6 | " | |
| " | 5, | 11 | " | 121 | " | 5 | " | |
| 41 | racemes, | 367 | pods, | 23 | failed, | or 6.2 per cent. |
According to these figures, not more than 6.2 per cent. of the ovaries failed to be fertilized.
While Cassia chamæcrista is usually abundant in Douglas county, owing, probably, largely to the severe drought, opportunities for study were not nearly so favorable as for Solanum. The material studied was found growing, for the most part, in somewhat shaded localities on the banks of Lake View.
Professor Todd has given very well the points in the structure of the flower of this species. He says: “The points that are of interest to us are the sickle-shaped pistil, the stamens with long, rigid anthers opening by terminal pores, and the most of them pointed toward the incurved petal, which is always on the opposite side from the pistil.”
The flowers are arranged in small clusters a little above the axils of the leaves. In some cases the axillary bud also develops into a flower cluster. The axillary clusters have been considered separately in the calculations made upon the conditions of the flowers.
Owing to the lack of material, Professor Todd was unable to determine any definite law governing the arrangement of the flowers in C. chamæcrista. This the writers have attempted to do. The determination of any law governing the order of development of the flowers in a plant like C. chamæcrista, where they are arranged in clusters developed from buds produced on the main axis, and the development of which is probably accelerated or retarded by various conditions, is much more difficult than in S. rostratum, where they are produced on a definite raceme, which is early differentiated from the terminal growing point, and at first develops more rapidly than the bud which is to continue the main axis of the branch.[R]
TABLE D. (Part 1)
| Cluster | 1 | 2 | 3 | 4 | 5 | 6 | |
| plant. | |||||||
| I | { 1 | A | 2b | b, 5p | b, l, p | A | A |
| { 2 | l, p | 2p | A | 3p | p | A | |
| { 3 | p | 3p | 4p | b, 3p | br, 4p | b, r, p | |
| II - | 1 | 2b | b, 3p, a | b, 2p, a | 2b, 3p | 2b, 3p | r |
| III - | 1 | 3b | 2b, p | b, 2p | 2b, 2p | b, br, p | b, 3p |
| IV | { 1 | b | 2b, bl | 2b, r | 2b, bl | 3b | 3b, br |
| { 2 | A | b, bl | 3b,bl | 3b, p | 3b | 3b, r, p | |
| V - | 1 | A | 2b, p | b, l, p | b, p | b, r, p | 2b, 2p |
| VI | { 1 | A | A | A | A | p | 2p, a |
| { 2 | A | p | b, 3p | b, 2p | 2b, 3p | 2b, p | |
| VII - | 1 | b, bl, 2p | 2b, 2p | b, l, p | 2b, bl, 2p | b, r, 2p | 2b, br, p |
| VIII | { 1 | 2b | 2b | 2b | 2b | 2b | |
| { 2 | b | 2b, lp | b, l, p | 2b, r, p | 3b, br | { 2b, l { b | |
| IX | { 1 | 2p | b, br, 2p | absent | 2b, 3p | b, r, 2p | 2b, a |
| { 2 | b, 3p | 2b, 4p | b, l, 3p | 2b, 2p | b, 3p | 2b, bl, 2p | |
| { 3 | A | 2b, 3p | 2b, p | 2b, p, a | 2b, 3p | 2b, p | |
| { 4 | A | b, 2p | b, p | b, r, 2p | b, 3p | b, p, a | |
| X | { 1 | 2b, 1p | 2b | 2b, p | b, 2p | br, p | b, br, p |
| { 2 | A | A | b | b, a | b, p | 2b, p | |
TABLE D. (Part 2)
| Cluster | 7 | 6 | 9 | 10 | 11 | 12 | |
| plant. | |||||||
| I | { 1 | A | A | A | b, 2p | 2b, 2p | 2b, 2p |
| { 2 | A | 2b, lp | b | A | 3b, p | { 2b { lb | |
| { 3 | b, 4p | 2b,bl, 3p | 2b, br, 2p, a | 2b, p, a | b, l, 2p | 2b, bl, p | |
| II - | 1 | 2b, br | 2b, br | b, r, p | 2b, bl | 3b | 2b |
| III - | 1 | b, 3p | 4p | b, r, 3p | b, bl, 3p | b, 3p | 3b, 2p |
| IV | { 1 | 2b, l | 3b | 3b | 3b | 3b | 3b |
| { 2 | 3b, br | 3b, l | 4b | 4b | 4b | ||
| V - | 1 | b, bl, p | b, r, p | 2b, r | 2b | 2b | 2b |
| VI | { 1 | b, 3p | b, 3p, a | b, r, 3p | 2b, 2p | 2b, 3p | 3b, p |
| { 2 | b, r, p | 2b, p, a | 2b, l, p | 3b, p | 3b, r | 3b | |
| VII - | 1 | { 2b, l, p { 2b | 3b, bl | { 3b, r { b | 3b | 3b | 3b |
| VIII | { 1 | ||||||
| { 2 | { 3b { 2b | 3b b | |||||
| IX | { 1 | 2b, bl | 2b, r, p | 2b, a | 2b, l | 3b | 2b |
| { 2 | 2b, r | 2b, p | b, l, p | 2b, bl | 3b | 3b | |
| { 3 | b, 2p | l | 2b, 2p | b, br, 2p | 2b, 2p | 2b | |
| { 4 | b, r, 3p | b, 3p | |||||
| X | { 1 | b, bl, r | 2b, br | 2b | 2b | 2b | b, a |
| { 2 | b, r | 2b, a | l | 2b | 2b | ||
TABLE D. (Part 3)
| Cluster | 13 | 14 | 15 | 16 | 17 | 18 | |
| plant. | |||||||
| I | { 1 | l | b, 2p | 2b, 2p | 3b, 2p | { 3b, p { b | br, 2b, p b |
| { 2 | 3b, p | 2b, l, p | 2b, bl | 2b, r | { 3b { b | 2b | |
| { 3 | br, a | {2b, br, a {a | 2b, la | 2b | b | 2b | |
| II - | 1 | 2b | |||||
| III - | 1 | b, 3p | 2b, bl | 2b, p | 2b, r | b | b |
| IV | { 1 | ||||||
| { 2 | |||||||
| V - | 1 | ||||||
| VI | { 1 | 3b, a | 3b, a | 2b, l | 3b | 3b | 3b |
| { 2 | 3b | 3b | 2b | ||||
| VII - | 1 | 2b | 2b | ||||
| VIII | { 1 | ||||||
| { 2 | |||||||
| IX | { 1 | ||||||
| { 2 | 3b | ||||||
| { 3 | 2b, p | 2b, a | 3b | 2b | |||
| { 4 | |||||||
| X | { 1 | ||||||
| { 2 | |||||||
TABLE D. (Part 4)
| Cluster | 19 | 20 | 21 | 22 | 23 | 24 | |
| plant. | |||||||
| I | { 1 | 3b, p | { 2b, br { b | 3b | { 3b { b | ||
| { 2 | 2b | ||||||
| { 3 | |||||||
| II - | 1 | ||||||
| III - | 1 | { 2b, 2p { b | b, l, p | { 2b, l { b | 3b, a | 2b, a | 2b |
| IV | { 1 | ||||||
| { 2 | |||||||
| V - | 1 | ||||||
| VI | { 1 | 3b | 3b | ||||
| { 2 | |||||||
| VII - | 1 | ||||||
| VIII | { 1 | ||||||
| { 2 | |||||||
| IX | { 1 | ||||||
| { 2 | |||||||
| { 3 | |||||||
| { 4 | |||||||
| X | { 1 | ||||||
| { 2 | |||||||
TABLE D. (Part 5)
| Cluster | |||||||
| plant. | |||||||
| I | { 1 | 6A, 35b, 2br, 2l, 21p. | |||||
| { 2 | 4A, 26b,1bl, 2l, 1r, 11p. | ||||||
| { 3 | 23b, 2bl, 4br, 1l, 1r, 31p, 5a. | ||||||
| II - | 1 | 22b, 2br, 1bl, 2r, 12p, 2a. | |||||
| III - | 1 | 41b, 2bl, 1br, 2l, 2r, 34p, 2a. | |||||
| IV | { 1 | 30b, 2bl, 1br, 1l, 1r, 2p. | |||||
| { 2 | 1A, 31b, 2b1, 1br, 1l, 1r, 2p. | ||||||
| V - | 1 | 1A, 17b, 1bl, 1l, 3r, 8p. | |||||
| VI | { 1 | 14A, 30b, 1l, 1r, 18p, 4a. | |||||
| { 2 | 1A, 28b, 1l, 2r, 14p, 1a. | ||||||
| VII - | 1 | 33b, 3bl, 1br, 2l, 2r, 11p. | |||||
| VIII | { 1 | 10b. | |||||
| { 2 | 21b, 1br, 2l, 1r, 3p. | ||||||
| IX | { 1 | 19b, 1bl, 1br, 1l, 2r, 10p, 2a. | |||||
| { 2 | 25b, 2bl, 2l, 1r, 19p. | ||||||
| { 3 | 1A, 27b, 1br, 1l, 18p, 2a. | ||||||
| { 4 | 1A, 7b, 2r, 15p, 1a. | ||||||
| X | { 1 | 18b, 1bl, 3br, 1r, 6p, 1a. | |||||
| { 2 | 2A, 12b, 1l, 1r, 2p, 2a. | ||||||
| 21A, 455b, 18br, 18bl, 21l, 24r, 234p, 22a. | |||||||
Abundant material in apparently the best condition was found growing around Lake View. Ten plants from this locality were examined, and their condition is here given in tabulated form. In the table following, the number of the plant is given in Roman numerals, the numbers of the branches following it in Arabic numerals. Beginning with the lower portion of the branch and passing upward, the flower clusters are numbered consecutively. These numbers, designated by “cluster,” are given in the first line at the top of the table. In the column beneath each of these numbers is shown the condition of the flowers of that cluster on the different branches of the different plants. The table was arranged in this form, not because a comparison of the condition of clusters of the same number is especially desired, but because this seemed the most compact form in which it could be arranged. In the columns under the different clusters, the condition of the flowers is designated as follows: r = right-, l = left-handed flower; b = bud; br and bl designate buds which are so well developed that it is possible to determine whether they are right-handed or left-handed—these buds will probably open the following morning; a=a bud or flower which has fallen off or failed to develop; A, indicates that the whole cluster has failed to develop. When an axillary cluster is developed it is included in a brace, with the cluster occurring immediately above it, the axillary cluster always being placed below. A seed pod is designated by p.
In the last column to the right the condition of each branch is summarized, and finally the grand total is given at the foot of the column.
In table D we have taken into account 241 flower clusters, and 21 which are either abortive or injured. The number of abortive clusters might be somewhat increased if great care had been exercised in looking for the accessory buds just above the axils of the lowest leaves on the branches. As a rule, however, the first internode or so, if questionable, was omitted. From this it would seem that about eight per cent. of the clusters fail to develop, a percentage which would probably be somewhat increased if care had been exercised in noting the buds where development had been arrested at a very early stage.
On the 10 plants, 14 axillary clusters were produced, being 5.5 per cent. of all the developed clusters. Of these 14 clusters, 2 produced 2 buds each, the others only 1; an average of 1.14 flowers per cluster. The 241 normally developed clusters produced 773 buds, an average of 3.27 flowers per cluster. Of the 773 buds produced on the 10 plants, 22 are found to be injured and fail to develop normally; a percentage of 2.84.
While the series of material is too limited to permit of indulging in generalizations, it might be of interest to note that on 40 plants bearing 332 seed pods, taken from two square feet of ground, September 4, and 3 other plants producing 130 seed pods, taken at the same time, not a single pod developed from an axillary cluster was found. These plants, however, with the exception of the last three, represent all produced on a definite area. It might not be improbable that the smaller, crowded plants would not be so likely to produce axillary clusters as the larger plants growing under more favorable conditions. We may at least conclude from this that the axillary flowers are of little consequence in the seed-producing capacity of the plant.
For the sake of convenience, it has been deemed advisable to summarize in table E the conditions of the flowers and buds which will probably open the day following, as given in table D. From this table, it will be seen that on the day the plants were examined 42 flowers were open—5.4 per cent. of the 773 buds produced on the 10 plants. These flowers as well as the buds, 36 in number, which were to open the next day, are equally divided into right-and left-handed.
The buds which are next to open do not, in any of the cases noted in the above tables, occur on a cluster with flowers which are already open.
| TABLE E. | |||||||||
| Plant I, | 6r | buds, | 3l | buds, | 2r | flowers, | 5l | flowers. | |
| II, | 2r | " | 1l | " | 2r | " | 0l | " | |
| III, | 1r | " | 2l | " | 2r | " | 2l | " | |
| IV, | 2r | " | 4l | " | 2r | " | 2l | " | |
| V, | 0r | " | 1l | " | 3r | " | 1l | " | |
| VI, | 0r | " | 0l | " | 3r | " | 2l | " | |
| VII, | 1r | " | 3l | " | 2r | " | 2l | " | |
| VIII, | 1r | " | 0l | " | 1r | " | 2l | " | |
| IX, | 2r | " | 3l | " | 5r | " | 4l | " | |
| X, | 3r | " | 1l | " | 2r | " | 1l | " | |
| 18r | buds, | 18l | buds, | 24r | flowers, | 21l | flowers. | ||
There seems to be no law governing the production of right-and left-handed flowers on the opposite sides of the main axis of the plant. Sometimes two right-or left-handed flowers will be produced in succession on one side of the raceme, and sometimes right-and left-handed alternate on the same side.
Concerning the method of pollination in C. chamæcrista, the writers have not been able to thoroughly satisfy themselves. Todd says: “I consider the following explanation most probable: In getting the pollen, some grains are dropped on the incurved petal, and by it made to adhere to points of the bee, and to such points in a right-handed flower as will carry it to the stigma of a left-handed flower, and vice versa.” Robertson[S] says: “The pollen, being thus forced out of the terminal anther pores, falls either directly upon the bee or upon the lateral petal which is pressed close against the bee’s side. In this way the side of the bee which is to the incurved petal receives the most pollen.... A bee visiting a left-hand flower receives pollen upon the right side and then flying to a right-hand flower strikes the same side against the stigma.”
It is very difficult to see just what takes place when the flowers are visited by a large insect, but the writers have observed that when they are visited by honey-bees, for instance, the insect supports itself by hooking his left hind leg over the terminal, upturned portion of the stigma in a right-handed flower, and the right leg in a left-handed flower. The pistil then would serve the function of support for the insect visitor. It was noticed that sometimes bees would attempt to get the pollen by approaching the flower from some direction other than that described above. The insect usually failed in this, and after one or two unsuccessful endeavors would give up the attempt and support itself by placing the leg over the terminal portion of the pistil while it secured the pollen. The function of the incurved petal is not perfectly clear. With an insect well dusted over with pollen from both right-and left-handed flowers, it seems improbable that cross-fertilization in any considerable number of cases should occur from some grains dropped on the incurved pistil.
The writers are not sure that the insect in flying to another flower strikes the tip of the pistil against the side, as stated by Robertson. Certainly, in many cases, the insect, while collecting the pollen, supports itself by placing one leg over the tip of the pistil. When the leg bears a large mass of pollen, which is being stored there, it seems hardly possible that the flowers could fail to be pollinated. It might be suggested that, since the stamens for the most part point in the direction of the incurved petal, the function of this petal is to prevent access to the stamens, except in the cases in which the insect supports itself by means of the pistil. While this seems to the writers, at the present time, the most logical of the two functions so far suggested, much more careful observation work must be done before this point is finally decided. The petal may to a certain extent, in connection with the pistil, serve as support for the insect. Todd and Robertson observed only humblebees visiting the flowers. The writers obtained:
- Apis mellifica Linn. Lake View, August 7. Seven specimens.
- Agapostemon texanus Cress. Lake View, August 7.
- Mellisoides bimaculata (St. Farg) Lepl. Lake View, August 7.
- Megachile petulans Cress. Lake View, August 7.
- Bombus separatus Cress. Lake View, August 7.
As in the case of Solanum, it will be seen that the collecting period extended over a very short period of time. More search would doubtless greatly increase the list.
Robertson reports the following species as collecting pollen: Bombus virginicus Oliv., B. separatus Cress., B. americanorum F., and B. scutellaris Cress.
August 28, when the blossoming season for C. chamæcrista was almost over, an examination of material from the above-named region was made for the purpose of determining the number of seeds produced by a single plant. Fifteen pods were selected at random from different plants and the number of ovules counted. It was impossible to tell about the number in each pod which were fully and normally developed seeds or which would become such; consequently this factor is not taken into consideration. The percentage of ovules which fail to develop is, however, small. The number of seeds found to the pod is shown by the following:
| TABLE F. | |||
| Pod I, | 13 | seeds. | |
| II, | 14 | " | |
| III, | 11 | " | |
| IV, | 11 | " | |
| V, | 10 | " | |
| VI, | 12 | " | |
| VII, | 16 | " | |
| VIII, | 12 | " | |
| IX, | 8 | " | |
| X, | 14 | " | |
| XI, | 17 | " | |
| XII, | 18 | " | |
| XIII, | 17 | " | |
| XIV, | 15 | " | |
| XV, | 14 | " | |
| Total XV, | 202 | seeds, | or 13.4 per pod. |
From this it will be seen that the minimum number of seeds found was 8, the maximum 18, with an average of 13.4. Since the pods were simply gathered at random, there is no certainty of gaining the maximum or minimum number of seeds, but a fair average of the number produced may be expected. September 4 three plants were examined to determine something about the range of variation in the number of ovules produced in the pods of a single plant. The results are given as follows:
- Plant 1 varies from 5 to 11.
- Plant 2 varies from 8 to 18.
- Plant 3 varies from 9 to 14.
- Plant 1 had 35 pods, plant 2 had 64, and plant 3 had 27.
- Plant 1 was selected on account of the small number of seeds produced per pod.
It will be seen from table D that an average of nearly 3.3 flower buds per cluster is produced. These were moderate-sized, healthy plants, producing on the whole probably more than the average number of clusters per plant. On the ten plants, there were produced 342 clusters, which bore 344 seed pods, instead of about 1120, the number of flowers which might be expected, thus giving less than thirty-three per cent. of the buds which produce mature seed pods.
It will be seen that, while in the observations made on S. rostratum the flowers which failed to produce seed did not reach much over six per cent., in C. chamæcrista it is over sixty per cent. In addition to this fact, it is rare to see a seed pod of S. rostratum which has been destroyed by insects or other destructive agencies, while in 460 pods of C. chamæcrista which were examined at Lake View, September 4, not one was found which did not have some of the ovules destroyed by the larvæ of some insect, and probably this would amount on the average to fifty per cent. of all the seeds produced, being in the case of some plants as high as seventy-five per cent.
A convenient method of approaching the question of the production of seeds might be to determine the number of seed pods produced on a given area of ground. A general idea may be obtained from the examination of the plants growing upon two square feet of ground. In the first case, the plants were much crowded; in the second, not nearly so much so; in fact, it may be said they were growing under “normal” conditions. It might be interesting to compare the results. The material for the two tables was taken September 4.
| FIRST SQUARE FOOT. | |||
| Plant | 1, | pods | 0 |
| " | 2, | " | 10 |
| " | 3, | " | 4 |
| " | 4, | " | 13 |
| " | 5, | " | 0 |
| " | 6, | " | 12 |
| " | 7, | " | 3 |
| " | 8, | " | 1 |
| " | 9, | " | 4 |
| " | 10, | " | 3 |
| " | 11, | " | 0 |
| " | 12, | " | 25 |
| " | 13, | " | 2 |
| " | 14, | " | 0 |
| " | 15, | " | 0 |
| " | 16, | " | 10 |
| " | 17, | " | 2 |
| " | 18, | " | 0 |
| " | 19, | " | 0 |
| " | 20, | " | 0 |
| " | 21, | " | 0 |
| " | 22, | " | 6 |
| " | 23, | " | 1 |
| " | 24, | " | 5 |
| " | 25, | " | 2 |
| " | 26, | " | 3 |
| " | 27, | " | 0 |
| " | 28, | " | 3 |
| Total, | 28, | pods | 109 |
SECOND SQUARE FOOT. | |||
| Plant | 1, | pods | 1 |
| " | 2, | " | 50 |
| " | 3, | " | 36 |
| " | 4, | " | 15 |
| " | 5, | " | 48 |
| " | 6, | " | 34 |
| " | 7, | " | 9 |
| " | 8, | " | 11 |
| " | 9, | " | 9 |
| " | 10, | " | 3 |
| " | 11, | " | 0 |
| " | 12, | " | 7 |
| Total, | 12, | pods | 223 |
In the first square foot of ground, where the plants were much crowded, of the twenty-eight plants, ten produced no seed pods at all, and of the remaining eighteen only six produced over five each. On these plants an average of a little less than four pods per plant was produced. In the second lot, where, evidently, the plants were not nearly so crowded, only four produced fewer than five seed pods, and there was a general average of 18.7 pods per plant.
On the first foot of ground, then, there might be produced in the neighborhood of 1300 seeds; on the second, 2600. The large Solanum upon which 40,000 seeds were estimated would probably cover an area of 12.5 square feet, giving 3200 seeds per square foot. Of course, these figures represent only certain isolated cases, which in a way are typical, but must not be taken to represent the average condition.
The largest plant noted September 4 had produced 100 pods, with an average of thirteen seeds per pod; this plant might show 1300 seeds.
Professor Todd discusses in his paper the occurrence of similar divergences from the typical form in other Solanaceæ and Leguminosæ, and tries to discover some hint as to their origin. Lack of material for observation precludes any present discussion of these points.
The results of these observations may be briefly summarized as follows: