MONOCOTYLEDONS.
JUNCEAE: Juncus.
GRAMINEAE: Leersia. Hordeum. Cryptostachys.
COMMELINEAE: Commelina.
PONTEDERACEAE: Monochoria.
ORCHIDEAE: Schomburgkia. Cattleya. Epidendron. Thelymitra.
The first point that strikes us in considering this list of 55 genera, is that they are very widely distributed in the vegetable series. They are more common in the family of the Leguminosae than in any other, and next in order in that of the Acanthaceae and Malpighiaceae. A large number, but not all the species, of certain genera, as of Oxalis and Viola, bear cleistogamic as well as ordinary flowers. A second point which deserves notice is that a considerable proportion of the genera produce more or less irregular flowers; this is the case with about 32 out of the 55 genera, but to this subject I shall recur.
I formerly made many observations on cleistogamic flowers, but only a few of them are worth giving, since the appearance of an admirable paper by Hugo Von Mohl, whose examination was in some respects much more complete than mine. (8/4. ‘Botanische Zeitung’ 1863 page 309-28.) His paper includes also an interesting history of our knowledge on the subject.
Viola canina.
The calyx of the cleistogamic flowers differs in no respect from that of the perfect ones. The petals are reduced to five minute scales; the lower one, which represents the lower lip, is considerably larger than the others, but with no trace of the spur-like nectary; its margins are smooth, whilst those of the other four scale-like petals are papillose. D. Muller of Upsala says that in the specimens which he observed the petals were completely aborted. (8/5. Ibid. 1857 page 730. This paper contains the first full and satisfactory account of any cleistogamic flower.) The stamens are very small, and only the two lower ones are provided with anthers, which do not cohere together as in the perfect flowers. The anthers are minute, with the two cells or loculi remarkably distinct; they contain very little pollen in comparison with those of the perfect flowers. The connective expands into a membranous hood-like shield which projects above the anther-cells. These two lower stamens have no vestige of the curious appendages which secrete nectar in the perfect flowers. The three other stamens are destitute of anthers and have broader filaments, with their terminal membranous expansions flatter or not so hood-like as those of the two antheriferous stamens. The pollen-grains have remarkably thin transparent coats; when exposed to the air they shrivel up quickly; when placed in water they swell, and are then 8-10/7000 of an inch in diameter, and therefore of smaller size than the ordinary pollen-grains similarly treated, which have a diameter of 13-14/7000 of an inch. In the cleistogamic flowers, the pollen-grains, as far as I could see, never naturally fall out of the anther-cells, but emit their tubes through a pore at the upper end. I was able to trace the tubes from the grains some way down the stigma. The pistil is very short, with the style hooked, so that its extremity, which is a little enlarged or funnel-shaped and represents the stigma, is directed downwards, being covered by the two membranous expansions of the antheriferous stamens. It is remarkable that there is an open passage from the enlarged funnel-shaped extremity to within the ovarium; this was evident, as slight pressure caused a bubble of air, which had been drawn in by some accident, to travel freely from one end to the other: a similar passage was observed by Michalet in V. alba. The pistil therefore differs considerably from that of the perfect flower; for in the latter it is much longer, and straight with the exception of the rectangularly bent stigma; nor is it perforated by an open passage.
The ordinary or perfect flowers have been said by some authors never to produce capsules; but this is an error, though only a small proportion of them do so. This appears to depend in some cases on their anthers not containing even a trace of pollen, but more generally on bees not visiting the flowers. I twice covered with a net a group of flowers, and marked with threads twelve of them which had not as yet expanded. This precaution is necessary, for though as a general rule the perfect flowers appear considerably before the cleistogamic ones, yet occasionally some of the latter are produced early in the season, and their capsules might readily be mistaken for those produced by the perfect flowers. Not one of the twelve marked perfect flowers yielded a capsule, whilst others under the net which had been artificially fertilised produced five capsules; and these contained exactly the same average number of seeds as some capsules from flowers outside the net which had been fertilised by bees. I have repeatedly seen Bombus hortorum, lapidarius, and a third species, as well as hive-bees, sucking the flowers of this violet: I marked six which were thus visited, and four of them produced fine capsules; the two others were gnawed off by some animal. I watched Bombus hortorum for some time, and whenever it came to a flower which did not stand in a convenient position to be sucked, it bit a hole through the spur-like nectary. Such ill-placed flowers would not yield any seed or leave descendants; and the plants bearing them would thus tend to be eliminated through natural selection.
The seeds produced by the cleistogamic and perfect flowers do not differ in appearance or number. On two occasions I fertilised several perfect flowers with pollen from other individuals, and afterwards marked some cleistogamic flowers on the same plants; and the result was that 14 capsules produced by the perfect flowers contained on an average 9.85 seeds; and 17 capsules from the cleistogamic ones contained 9.64 seeds,—an amount of difference of no significance. It is remarkable how much more quickly the capsules from the cleistogamic flowers are developed than those from the perfect ones; for instance, several perfect flowers were cross-fertilised on April 14th, 1863, and a month afterwards (May 15th) eight young cleistogamic flowers were marked with threads; and when the two sets of capsules thus produced were compared on June 3rd, there was scarcely any difference between them in size.
Viola odorata (WHITE-FLOWERED, SINGLE, CULTIVATED VARIETY).
The petals are represented by mere scales as in the last species; but differently from in the last, all five stamens are provided with diminutive anthers. Small bundles of pollen-tubes were traced from the five anthers into the somewhat distant stigma. The capsules produced by these flowers bury themselves in the soil, if it be loose enough, and there mature themselves. (8/6. Vaucher says ‘Hist. Phys. des Plantes d’Europe’ tome 3 1844 page 309, that V. hirta and collina likewise bury their capsules. See also Lecoq ‘Geograph. Bot.’ tome 5 1856 page 180.) Lecoq says that it is only these latter capsules which possess elastic valves; but I think this must be a misprint, as such valves would obviously be of no use to the buried capsules, but would serve to scatter the seeds of the sub-aerial ones, as in the other species of Viola. It is remarkable that this plant, according to Delpino, does not produce cleistogamic flowers in one part of Liguria, whilst the perfect flowers are there abundantly fertile (8/7. ‘Sull’ Opera, la Distribuzione dei Sessi nelle Piante’ etc. 1867 page 30.); on the other hand, cleistogamic flowers are produced by it near Turin. Another fact is worth giving as an instance of correlated development: I found on a purple variety, after it had produced its perfect double flowers, and whilst the white single variety was bearing its cleistogamic flowers, many bud-like bodies which from their position on the plant were certainly of a cleistogamic nature. They consisted, as could be seen on bisecting them, of a dense mass of minute scales closely folded over one another, exactly like a cabbage-head in miniature. I could not detect any stamens, and in the place of the ovarium there was a little central column. The doubleness of the perfect flowers had thus spread to the cleistogamic ones, which therefore were rendered quite sterile.
Viola hirta.
The five stamens of the cleistogamic flowers are provided, as in the last case, with small anthers, from all of which pollen-tubes proceed to the stigma. The petals are not quite so much reduced as in V. canina, and the short pistil instead of being hooked is merely bent into a rectangle. Of several perfect flowers which I saw visited by hive-and humble-bees, six were marked, but they produced only two capsules, some of the others having been accidentally injured. M. Monnier was therefore mistaken in this case as in that of V. odorata, in supposing that the perfect flowers always withered away and aborted. He states that the peduncles of the cleistogamic flowers curve downwards and bury the ovaries beneath the soil. (8/8. These statements are taken from Professor Oliver’s excellent article in the ‘Natural History Review’ July 1862 page 238. With respect to the supposed sterility of the perfect flowers in this genus see also Timbal-Lagrave ‘Botanische Zeitung’ 1854 page 772.) I may here add that Fritz Muller, as I hear from his brother, has found in the highlands of Southern Brazil a white-flowered species of violet which bears subterranean cleistogamic flowers.
Viola nana.
Mr. Scott sent me seeds of this Indian species from the Sikkim Terai, from which I raised many plants, and from these other seedlings during several successive generations. They produced an abundance of cleistogamic flowers during the whole of each summer, but never a perfect one. When Mr. Scott wrote to me his plants in Calcutta were behaving similarly, though his collector saw the species in flower in its native site. This case is valuable as showing that we ought not to infer, as has sometimes been done, that a species does not bear perfect flowers when growing naturally, because it produces only cleistogamic flowers under culture. The calyx of these flowers is sometimes formed of only three sepals; two being actually suppressed and not merely coherent with the others; this occurred with five out of thirty flowers which were examined for this purpose. The petals are represented by extremely minute scales. Of the stamens, two bear anthers which are in the same state as in the previous species, but, as far as I could judge, each of the two cells contained only from 20 to 25 delicate transparent pollen-grains. These emitted their tubes in the usual manner. The three other stamens bore very minute rudimentary anthers, one of which was generally larger than the other two, but none of them contained any pollen. In one instance, however, a single cell of the larger rudimentary anther included a little pollen. The style consists of a short flattened tube, somewhat expanded at its upper end, and this forms an open channel leading into the ovarium, as described under V. canina. It is slightly bent towards the two fertile anthers.
Viola Roxburghiana.
This species bore in my hothouse during two years a multitude of cleistogamic flowers, which resembled in all respects those of the last species; but no perfect ones were produced. Mr. Scott informs me that in India it bears perfect flowers only during the cold season, and that these are quite fertile. During the hot, and more especially during the rainy season, it bears an abundance of cleistogamic flowers.
Many other species, besides the five now described, produce cleistogamic flowers; this is the case, according to D. Muller, Michalet, Von Mohl, and Hermann Muller, with V. elatior, lancifolia, sylvatica, palustris, mirabilis, bicolor, ionodium, and biflora. But V. tricolor does not produce them.
Michalet asserts that V. palustris produces near Paris only perfect flowers, which are quite fertile; but that when the plant grows on mountains cleistogamic flowers are produced; and so it is with V. biflora. The same author states that he has seen in the case of V. alba flowers intermediate in structure between the perfect and cleistogamic ones. According to M. Boisduval, an Italian species, V. Ruppii, never bears in France “des fleurs bien apparentes, ce qui ne l’empeche pas de fructifier.”
It is interesting to observe the gradation in the abortion of the parts in the cleistogamic flowers of the several foregoing species. It appears from the statements by D. Muller and Von Mohl that in V. mirabilis the calyx does not remain quite closed; all five stamens are provided with anthers, and some pollen-grains probably fall out of the cells on the stigma, instead of protruding their tubes whilst still enclosed, as in the other species. In V. hirta all five stamens are likewise antheriferous; the petals are not so much reduced and the pistil not so much modified as in the following species. In V. nana and elatior only two of the stamens properly bear anthers, but sometimes one or even two of the others are thus provided. Lastly, in V. canina never more than two of the stamens, as far as I have seen, bear anthers; the petals are much more reduced than in V. hirta, and according to D. Muller are sometimes quite absent.
Oxalis acetosella.
The existence of cleistogamic flowers on this plant was discovered by Michalet. (8/9. ‘Bulletin Soc. Bot. de France’ tome 7 1860 page 465.) They have been fully described by Von Mohl, and I can add hardly anything to his description. In my specimens the anthers of the five longer stamens were nearly on a level with the stigmas; whilst the smaller and less plainly bilobed anthers of the five shorter stamens stood considerably below the stigmas, so that their tubes had to travel some way upwards. According to Michalet these latter anthers are sometimes quite aborted. In one case the tubes, which ended in excessively fine points, were seen by me stretching upwards from the lower anthers towards the stigmas, which they had not as yet reached. My plants grew in pots, and long after the perfect flowers had withered they produced not only cleistogamic but a few minute open flowers, which were in an intermediate condition between the two kinds. In one of these the pollen-tubes from the lower anthers had reached the stigmas, though the flower was open. The footstalks of the cleistogamic flowers are much shorter than those of the perfect flowers, and are so much bowed downwards that they tend, according to Von Mohl, to bury themselves in the moss and dead leaves on the ground. Michalet also says that they are often hypogean. In order to ascertain the number of seeds produced by these flowers, I marked eight of them; two failed, one cast its seed abroad, and the remaining five contained on an average 10.0 seeds per capsule. This is rather above the average 9.2, which eleven capsules from perfect flowers fertilised with their own pollen yielded, and considerably above the average 7.9, from the capsules of perfect flowers fertilised with pollen from another plant; but this latter result must, I think, have been accidental.
Hildebrand, whilst searching various Herbaria, observed that many other species of Oxalis besides O. acetosella produce cleistogamic flowers (8/10. ‘Monatsbericht der Akad. der Wiss. zu Berlin’ 1866 page 369.); and I hear from him that this is the case with the heterostyled trimorphic O. incarnata from the Cape of Good Hope.
Oxalis (Biophytum) sensitiva.
This plant is ranked by many botanists as a distinct genus, but as a sub-genus by Bentham and Hooker. Many of the early flowers on a mid-styled plant in my hothouse did not open properly, and were in an intermediate condition between cleistogamic and perfect. Their petals varied from a rudiment to about half their proper size; nevertheless they produced capsules. I attributed their state to unfavourable conditions, for later in the season fully expanded flowers of the proper size appeared. But Mr. Thwaites afterwards sent me from Ceylon a number of long-styled, mid-styled, and short-styled flower-stalks preserved in spirits; and on the same stalks with the perfect flowers, some of which were fully expanded and others still in bud, there were small bud-like bodies containing mature pollen, but with their calyces closed. These cleistogamic flowers do not differ much in structure from the perfect ones of the corresponding form, with the exception that their petals are reduced to extremely minute, barely visible scales, which adhere firmly to the rounded bases of the shorter stamens. Their stigmas are much less papillose, and smaller in about the ratio of 13 to 20 divisions of the micrometer, as measured transversely from apex to apex, than the stigmas of the perfect flowers. The styles are furrowed longitudinally, and are clothed with simple as well as glandular hairs, but only in the cleistogamic flowers produced by the long- styled and mid-styled forms. The anthers of the longer stamens are a little smaller than the corresponding ones of the perfect flowers, in about the ratio of 11 to 14. They dehisce properly, but do not appear to contain much pollen. Many pollen-grains were attached by short tubes to the stigmas; but many others, still adhering to the anthers, had emitted their tubes to a considerable length, without having come in contact with the stigmas. Living plants ought to be examined, as the stigmas, at least of the long-styled form, project beyond the calyx, and if visited by insects (which, however, is very improbable) might be fertilised with pollen from a perfect flower. The most singular fact about the present species is that long-styled cleistogamic flowers are produced by the long-styled plants, and mid-styled as well as short-styled cleistogamic flowers by the other two forms; so that there are three kinds of cleistogamic and three kinds of perfect flowers produced by this one species! Most of the heterostyled species of Oxalis are more or less sterile, many absolutely so, if illegitimately fertilised with their own-form pollen. It is therefore probable that the pollen of the cleistogamic flowers has been modified in power, so as to act on their own stigmas, for they yield an abundance of seeds. We may perhaps account for the cleistogamic flowers consisting of the three forms, through the principle of correlated growth, by which the cleistogamic flowers of the double violet have been rendered double.
Vandellia nummularifolia.
Dr. Kuhn has collected all the notices with respect to cleistogamic flowers in this genus, and has described from dried specimens those produced by an Abyssinian species. (8/11. ‘Botanische Zeitung’ 1867 page 65.) Mr. Scott sent me from Calcutta seeds of the above common Indian weed, from which many plants were successively raised during several years. The cleistogamic flowers are very small, being when fully mature under 1/20 of an inch (1.27 millimetres) in length. The calyx does not open, and within it the delicate transparent corolla remains closely folded over the ovarium. There are only two anthers instead of the normal number of four, and their filaments adhere to the corolla. The cells of the anthers diverge much at their lower ends and are only 5/700 of an inch (.181 millimetres) in their longer diameter. They contain but few pollen-grains, and these emit their tubes whilst still within the anther. The pistil is very short, and is surmounted by a bilobed stigma. As the ovary grows the two anthers together with the shrivelled corolla, all attached by the dried pollen-tubes to the stigma, are torn off and carried upwards in the shape of a little cap. The perfect flowers generally appear before the cleistogamic, but sometimes simultaneously with them. During one season a large number of plants produced no perfect flowers. It has been asserted that the latter never yield capsules; but this is a mistake, as they do so even when insects are excluded. Fifteen capsules from cleistogamic flowers on plants growing under favourable conditions contained on an average 64.2 seeds, with a maximum of 87; whilst 20 capsules from plants growing much crowded yielded an average of only 48. Sixteen capsules from perfect flowers artificially crossed with pollen from another plant contained on an average 93 seeds, with a maximum of 137. Thirteen capsules from self-fertilised perfect flowers gave an average of 62 seeds, with a maximum of 135. Therefore the capsules from the cleistogamic flowers contained fewer seeds than those from perfect flowers when cross-fertilised, and slightly more than those from perfect flowers self-fertilised.
Dr. Kuhn believes that the Abyssinian V. sessiflora does not differ specifically from the foregoing species. But its cleistogamic flowers apparently include four anthers instead of two as above described. The plants, moreover, of V. sessiflora produce subterranean runners which yield capsules; and I never saw a trace of such runners in V. nummularifolia, although many plants were cultivated.
Linaria spuria.
Michalet says that short, thin, twisted branches are developed from the buds in the axils of the lower leaves, and that these bury themselves in the ground. (8/12. ‘Bulletin Soc. Bot. de France’ tome 7 1860 page 468.) They there produce flowers not offering any peculiarity in structure, excepting that their corollas, though properly coloured, are deformed. These flowers may be ranked as cleistogamic, as they are developed, and not merely drawn, beneath the ground.
Ononis columnae.
Plants were raised from seeds sent me from Northern Italy. The sepals of the cleistogamic flowers are elongated and closely pressed together; the petals are much reduced in size, colourless, and folded over the interior organs. The filaments of the ten stamens are united into a tube, and this is not the case, according to Von Mohl, with the cleistogamic flowers of other Leguminosae. Five of the stamens are destitute of anthers, and alternate with the five thus provided. The two cells of the anthers are minute, rounded and separated from one another by connective tissue; they contain but few pollen-grains, and these have extremely delicate coats. The pistil is hook-shaped, with a plainly enlarged stigma, which is curled down, towards the anthers; it therefore differs much from that of the perfect flower. During the year 1867 no perfect flowers were produced, but in the following year there were both perfect and cleistogamic ones.
Ononis minutissima.
My plants produced both perfect and cleistogamic flowers; but I did not examine the latter. Some of the former were crossed with pollen from a distinct plant, and six capsules thus obtained yielded on an average 3.66 seeds, with a maximum of 5 in one. Twelve perfect flowers were marked and allowed to fertilise themselves spontaneously under a net, and they yielded eight capsules, containing on an average 2.38 seeds, with a maximum of 3 in one. Fifty-three capsules produced by the cleistogamic flowers contained on an average 4.1 seeds, so that these were the most productive of all; and the seeds themselves looked finer even than those from the crossed perfect flowers. According to Mr. Bentham O. parviflora likewise bears cleistogamic flowers; and he informs me that these flowers are produced by all three species early in the spring; whilst the perfect ones appear afterwards, and therefore in a reversed order compared with those of Viola and Oxalis. Some of the species, for instance Ononis columnae, bear a fresh crop of cleistogamic flowers in the autumn.
Lathyrus nissolia.
This plant apparently offers a case of the first stage in the production of cleistogamic flowers, for on plants growing in a state of nature, many of the flowers never expand and yet produce fine pods. Some of the buds are so large that they seem on the point of expansion; others are much smaller, but none so small as the true cleistogamic flowers of the foregoing species. As I marked these buds with thread and examined them daily, there could be no mistake about their producing fruit without having expanded.
Several other Leguminous genera produce cleistogamic flowers, as may be seen in Table 8.38; but much does not appear to be known about them. Von Mohl says that their petals are commonly rudimentary, that only a few of their anthers are developed, their filaments are not united into a tube and their pistils are hook-shaped. In three of the genera, namely Vicia, Amphicarpaea, and Voandzeia, the cleistogamic flowers are produced on subterranean stems. The perfect flowers of Voandzeia, which is a cultivated plant, are said never to produce fruit (8/13. Correa de Mello ‘Journal of the Linnean Society Botany’ volume 11 1870 page 254, particularly attended to the flowering and fruiting of this African plant, which is sometimes cultivated in Brazil.); but we should remember how often fertility is affected by cultivation.
Impatiens fulva.
Mr. A.W. Bennett has published an excellent description, with figures, of this plant. (8/14. ‘Journal of the Linnean Society Botany’ volume 13 1872 page 147.) He shows that the cleistogamic and perfect flowers differ in structure at a very early period of growth, so that the existence of the former cannot be due merely to the arrested development of the latter,—a conclusion which indeed follows from most of the previous descriptions. Mr. Bennett found on the banks of the Wey that the plants which bore cleistogamic flowers alone were to those bearing perfect flowers as 20 to 1; but we should remember that this is a naturalised species. The perfect flowers are usually barren in England; but Professor Asa Gray writes to me that after midsummer in the United States some or many of them produce capsules.
Impatiens noli-me-tangere.
I can add nothing of importance to Von Mohl’s description, excepting that one of the rudimentary petals shows a vestige of a nectary, as Mr. Bennett likewise found to be the case with I. fulva. As in this latter species all five stamens produce some pollen, though small in amount; a single anther contains, according to Von Mohl, not more than 50 grains, and these emit their tubes while still enclosed within it. The pollen-grains of the perfect flowers are tied together by threads, but not, so far as I could see, those of the cleistogamic flowers; and a provision of this kind would here have been useless, as the grains can never be transported by insects. The flowers of I. balsamina are visited by humble-bees (8/15. H. Muller ‘Die Befruchtung’ etc. page 170.), and I am almost sure that this is the case with the perfect flowers of I. noli-me-tangere. From the perfect flowers of this latter species covered with a net eleven spontaneously self-fertilised capsules were produced, and these yielded on an average 3.45 seeds. Some perfect flowers with their anthers still containing an abundance of pollen were fertilised with pollen from a distinct plant; and the three capsules thus produced contained, to my surprise, only 2, 2, and 1 seed. As I. balsamina is proterandrous, so probably is the present species; and if so, cross-fertilisation was effected by me at too early a period, and this may account for the capsules yielding so few seeds.
Drosera rotundifolia.
The first flower-stems which were thrown up by some plants in my greenhouse bore only cleistogamic flowers. The petals of small size remained permanently closed over the reproductive organs, but their white tips could just be seen between the almost completely closed sepals. The pollen, which was scanty in amount, but not so scanty as in Viola or Oxalis, remained enclosed within the anthers, whence the tubes proceeded and penetrated the stigma. As the ovarium swelled the little withered corolla was carried upwards in the form of a cap. These cleistogamic flowers produced an abundance of seed. Later in the season perfect flowers appeared. With plants in a state of nature the flowers open only in the early morning, as I have been informed by Mr. Wallis, who particularly attended to the time of their flowering. In the case of D. Anglica, the still folded petals on some plants in my greenhouse opened just sufficiently to leave a minute aperture; the anthers dehisced properly, but the pollen-grains adhered in a mass to them, and thence emitted their tubes, which penetrated the stigmas. These flowers, therefore, were in an intermediate condition, and could not be called either perfect or cleistogamic.
A few miscellaneous observations may be added with respect to some other species, as throwing light on our subject. Mr. Scott states that Eranthemum ambiguum bears three kinds of flowers,—large, conspicuous, open ones, which are quite sterile,—others of intermediate size, which are open and moderately fertile—and lastly small closed or cleistogamic ones, which are perfectly fertile. (8/16. ‘Journal of Botany’ London new series volume 1 1872 pages 161- 4.) Ruellia tuberosa, likewise one of the Acanthaceae, produces both open and cleistogamic flowers; the latter yield from 18 to 24, whilst the former only from 8 to 10 seeds; these two kinds of flowers are produced simultaneously, whereas in several other members of the family the cleistogamic ones appear only during the hot season. According to Torrey and Gray, the North American species of Helianthemum, when growing in poor soil, produce only cleistogamic flowers. The cleistogamic flowers of Specularia perfoliata are highly remarkable, as they are closed by a tympanum formed by the rudimentary corolla, and without any trace of an opening. The stamens vary from 3 to 5 in number, as do the sepals. (8/17. Von Mohl ‘Botanische Zeitung’ 1863 pages 314 and 323. Dr. Bromfield ‘Phytologist’ volume 3 page 530, also remarks that the calyx of the cleistogamic flowers is usually only 3-cleft, while that of the perfect flower is mostly 5- cleft.) The collecting hairs on the pistil, which play so important a part in the fertilisation of the perfect flowers, are here quite absent. Drs. Hooker and Thomson state that some of the Indian species of Campanula produce two kinds of flowers; the smaller ones being borne on longer peduncles with differently formed sepals, and producing a more globose ovary. (8/18. ‘Journal of the Linnean Society’ volume 2 1857 page 7. See also Professor Oliver in ‘Natural History Review’ 1862 page 240.) The flowers are closed by a tympanum like that in Specularia. Some of the plants produce both kinds of flowers, others only one kind; both yield an abundance of seeds. Professor Oliver adds that he has seen flowers on Campanula colorata in an intermediate condition between cleistogamic and perfect ones.
The solitary almost sessile cleistogamic flowers produced by Monochoria vaginalis are differently protected from those in any of the previous cases, namely, within “a short sack formed of the membranous spathe, without any opening or fissure.” There is only a single fertile stamen; the style is almost obsolete, with the three stigmatic surfaces directed to one side. Both the perfect and cleistogamic flowers produce seeds. (8/19. Dr. Kirk ‘Journal of the Linnean Society’ volume 8 1864 page 147.)
The cleistogamic flowers on some of the Malpighiaceae seem to be more profoundly modified than those in any of the foregoing genera. According to A. de Jussieu they are differently situated from the perfect flowers; they contain only a single stamen, instead of 5 or 6; and it is a strange fact that this particular stamen is not developed in the perfect flowers of the same species. (8/20. ‘Archives du Museum’ tome 3 1843 pages 35-38, 82-86, 589, 598.) The style is absent or rudimentary; and there are only two ovaries instead of three. Thus these degraded flowers, as Jussieu remarks, “laugh at our classifications, for the greater number of the characters proper to the species, to the genus, to the family, to the class disappear.” I may add that their calyces are not glandular, and as, according to Kerner, the fluid secreted by such glands generally serves to protect the flowers from crawling insects, which steal the nectar without aiding in their cross-fertilisation (8/21. ‘Die Schutzmittel der Bluthen gegen unberufene Gaste’ 1876 page 25.), the deficiency of the glands in the cleistogamic flowers of these plants may perhaps be accounted for by their not requiring any such protection.
As the Asclepiadous genus Stapelia is said to produce cleistogamic flowers, the following case may be worth giving. I have never heard of the perfect flowers of Hoya carnosa setting seeds in this country, but some capsules were produced in Mr. Farrer’s hothouse; and the gardener detected that they were the product of minute bud-like bodies, three or four of which could sometimes be found on the same umbel with the perfect flowers. They were quite closed and hardly thicker than their peduncles. The sepals presented nothing particular, but internally and alternating with them, there were five small flattened heart-shaped papillae, like rudiments of petals; but the homological nature of which appeared doubtful to Mr. Bentham and Dr. Hooker. No trace of anthers or of stamens could be detected; and I knew from having examined many cleistogamic flowers what to look for. There were two ovaries, full of ovules, quite open at their upper ends, with their edges festooned, but with no trace of a proper stigma. In all these flowers one of the two ovaries withered and blackened long before the other. The one perfect capsule, 3 1/2 inches in length, which was sent me, had likewise been developed from a single carpel. This capsule contained an abundance of plumose seeds, many of which appeared quite sound, but they did not germinate when sown at Kew. Therefore the little bud-like flower which produced this capsule probably was as destitute of pollen as were those which I examined.
Juncus bufonius and Hordeum.
All the species hitherto mentioned which produce cleistogamic flowers are entomophilous; but four genera, Juncus, Hordeum, Cryptostachys, and Leersia are anemophilous. Juncus bufonius is remarkable by bearing in parts of Russia only cleistogamic flowers, which contain three instead of the six anthers found in the perfect flowers. (8/22. See Dr. Ascherson’s interesting paper in ‘Botanische Zeitung’ 1871 page 551.) In the genus Hordeum it has been shown by Delpino that the majority of the flowers are cleistogamic, some of the others expanding and apparently allowing of cross-fertilisation. (8/23. ‘Bollettini del Comizio agrario Parmense.’ Marzo e Aprile 1871. An abstract of this valuable paper is given in ‘Botanische Zeitung’ 1871 page 537. See also Hildebrand on Hordeum in ‘Monatsbericht d. K. Akad Berlin’ October 1872 page 760.) I hear from Fritz Muller that there is a grass in Southern Brazil, in which the sheath of the uppermost leaf, half a metre in length, envelopes the whole panicle; and this sheath never opens until the self-fertilised seeds are ripe. On the roadside some plants had been cut down, whilst the cleistogamic panicles were developing, and these plants afterwards produced free or unenclosed panicles of small size, bearing perfect flowers.
Leersia oryzoides.
It has long been known that this plant produces cleistogamic flowers, but these were first described with care by M. Duval-Jouve. (8/24. ‘Bulletin Bot. Soc. de France’ tome 10 1863 page 194.) I procured plants from a stream near Reigate, and cultivated them for several years in my greenhouse. The cleistogamic flowers are very small, and usually mature their seeds within the sheaths of the leaves. These flowers are said by Duval-Jouve to be filled by slightly viscid fluid; but this was not the case with several that I opened; but there was a thin film of fluid between the coats of the glumes, and when these were pressed the fluid moved about, giving a similarly deceptive appearance of the whole inside of the flower being thus filled. The stigma is very small and the filaments extremely short; the anthers are less than 1/50 of an inch in length or about one-third of the length of those in the perfect flowers. One of the three anthers dehisces before the two others. Can this have any relation with the fact that in some other species of Leersia only two stamens are fully developed? (8/25. Asa Gray ‘Manual of Botany of the United States’ 1856 page 540.) The anthers shed their pollen on the stigma; at least in one instance this was clearly the case, and by tearing open the anthers under water the grains were easily detached. Towards the apex of the anther the grains are arranged in a single row and lower down in two or three rows, so that they could be counted; and there were about 35 in each cell, or 70 in the whole anther; and this is an astonishingly small number for an anemophilous plant. The grains have very delicate coats, are spherical and about 5/7000 of an inch (.0181 millimetres), whilst those of the perfect flowers are about 7/7000 of an inch (.0254 millimetres) in diameter.
M. Duval-Jouve states that the panicles very rarely protrude from their sheaths, but that when this does happen the flowers expand and exhibit well-developed ovaries and stigmas, together with full-sized anthers containing apparently sound pollen; nevertheless such flowers are invariably quite sterile. Schreiber had previously observed that if a panicle is only half protruded, this half is sterile, whilst the still included half is fertile. Some plants which grew in a large tub of water in my greenhouse behaved on one occasion in a very different manner. They protruded two very large much-branched panicles; but the florets never opened, though these included fully developed stigmas, and stamens supported on long filaments with large anthers that dehisced properly. If these florets had opened for a short time unperceived by me and had then closed again, the empty anthers would have been left dangling outside. Nevertheless they yielded on August 17th an abundance of fine ripe seeds. Here then we have a near approach to the single case as yet known of this grass producing in a state of nature (in Germany) perfect flowers which yielded a copious supply of fruit. (8/26. Dr. Ascherson ‘Botanische Zeitung’ 1864 page 350.) Seeds from the cleistogamic flowers were sent by me to Mr. Scott in Calcutta, who there cultivated the plants in various ways, but they never produced perfect flowers.
In Europe Leersia oryzoides is the sole representative of its genus, and Duval- Jouve, after examining several exotic species, found that it apparently is the sole one which bears cleistogamic flowers. It ranges from Persia to North America, and specimens from Pennsylvania resembled the European ones in their concealed manner of fructification. There can therefore be little doubt that this plant generally propagates itself throughout an immense area by cleistogamic seeds, and that it can hardly ever be invigorated by cross- fertilisation. It resembles in this respect those plants which are now widely spread, though they increase solely by asexual generation. (8/27. I have collected several such cases in my ‘Variation under Domestication’ chapter 18 2nd edition volume 2 page 153.)