CHAPTER VIII. CLEISTOGAMIC FLOWERS.
General character of cleistogamic flowers. List of the genera producing such flowers, and their distribution in the vegetable series. Viola, description of the cleistogamic flowers in the several species; their fertility compared with that of the perfect flowers. Oxalis acetosella. O. sensitiva, three forms of cleistogamic flowers. Vandellia. Ononis. Impatiens. Drosera. Miscellaneous observations on various other cleistogamic plants. Anemophilous species producing cleistogamic flowers. Leersia, perfect flowers rarely developed. Summary and concluding remarks on the origin of cleistogamic flowers. The chief conclusions which may be drawn from the observations in this volume.
It was known even before the time of Linnaeus that certain plants produced two kinds of flowers, ordinary open, and minute closed ones; and this fact formerly gave rise to warm controversies about the sexuality of plants. These closed flowers have been appropriately named cleistogamic by Dr. Kuhn. (8/1. 'Botanische Zeitung' 1867 page 65.) They are remarkable from their small size and from never opening, so that they resemble buds; their petals are rudimentary or quite aborted; their stamens are often reduced in number, with the anthers of very small size, containing few pollen-grains, which have remarkably thin transparent coats, and generally emit their tubes whilst still enclosed within the anther-cells; and, lastly, the pistil is much reduced in size, with the stigma in some cases hardly at all developed. These flowers do not secrete nectar or emit any odour; from their small size, as well as from the corolla being rudimentary, they are singularly inconspicuous. Consequently insects do not visit them; nor if they did, could they find an entrance. Such flowers are therefore invariably self-fertilised; yet they produce an abundance of seed. In several cases the young capsules bury themselves beneath the ground, and the seeds are there matured. These flowers are developed before, or after, or simultaneously with the perfect ones. Their development seems to be largely governed by the conditions to which the plants are exposed, for during certain seasons or in certain localities only cleistogamic or only perfect flowers are produced.
Dr. Kuhn, in the article above referred to, gives a list of 44 genera including species which bear flowers of this kind. To this list I have added some genera, and the authorities are appended in a footnote. I have omitted three names, from reasons likewise given in the footnote. But it is by no means easy to decide in all cases whether certain flowers ought to be ranked as cleistogamic. For instance, Mr. Bentham informs me that in the South of France some of the flowers on the vine do not fully open and yet set fruit; and I hear from two experienced gardeners that this is the case with the vine in our hothouses; but as the flowers do not appear to be completely closed it would be imprudent to consider them as cleistogamic. The flowers of some aquatic and marsh plants, for instance of Ranunculus aquatalis, Alisma natans, Subularia, Illecebrum, Menyanthes, and Euryale, remain closely shut as long as they are submerged, and in this condition fertilise themselves. (8/2. Delpino 'Sull' Opera, la Distribuzione dei Sessi nelle Piante' etc. 1867 page 30. Subularia, however, sometimes has its flowers fully expanded beneath the water, see Sir J.E. Smith 'English Flora' volume 3 1825 page 157. For the behaviour of Menyanthes in Russia see Gillibert in 'Act. Acad. St. Petersb.' 1777 part 2 page 45.--On Euryale 'Gardener's Chronicle' 1877 page 280.) They behave in this manner, apparently as a protection to their pollen, and produce open flowers when exposed to the air; so that these cases seem rather different from those of true cleistogamic flowers, and have not been included in the list. Again, the flowers of some plants which are produced very early or very late in the season do not properly expand; and these might perhaps be considered as incipiently cleistogamic; but as they do not present any of the remarkable peculiarities proper to the class, and as I have not found any full record of such cases, they are not entered in the list. When, however, it is believed on fairly good evidence that the flowers on a plant in its native country do not open at any hour of the day or night, and yet set seeds capable of germination, these may fairly be considered as cleistogamic, notwithstanding that they present no peculiarities of structure.