The Different Forms of Flowers on Plants of the Same Species Part 27

We should bear in mind that as the hermaphrodite is the normal form, its corolla has probably retained its original size. (7/24. It does not appear to me that Kerner's view 'Die Schutzmittel des Pollens' 1873 page 56, can be accepted in the present cases, namely that the larger corolla in the hermaphrodites and males serves to protect their pollen from rain. In the genus Thymus, for instance, the aborted anthers of the female are much better protected than the perfect ones of the hermaphrodite.) An objection to the above view should not be pa.s.sed over; namely, that the abortion of the stamens in the females ought to have added through the law of compensation to the size of the corolla; and this perhaps would have occurred, had not the expenditure saved by the abortion of the stamens been directed to the female reproductive organs, so as to give to this form increased fertility.

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 s.e.xuality 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 cla.s.s, 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. I will now give as complete a list of the genera containing cleistogamic species as I have been able to collect.

TABLE 8.38. List of genera including cleistogamic species (chiefly after Kuhn).

(8/3. I have omitted Trifolium and Arachis from the list, because Von Mohl says 'Botanische Zeitung' 1863 page 312, that the flower-stems merely draw the flowers beneath the ground, and that these do not appear to be properly cleistogamic. Correa de Mello 'Journal of the Linnean Society Botany' volume 11 1870 page 254, observed plants of Arachis in Brazil, and could never find such flowers. Plantago has been omitted because as far as I can discover it produces hermaphrodite and female flower-heads, but not cleistogamic flowers.

Krascheninikowia (vel Stellaria) has been omitted because it seems very doubtful from Maximowicz' description whether the lower flowers which have no petals or very small ones, and barren stamens or none, are cleistogamic; the upper hermaphrodite flowers are said never to produce fruit, and therefore probably act as males. Moreover in Stellaria graminea, as Babington remarks 'British Botany' 1851 page 51, "shorter and longer petals accompany an imperfection of the stamens or germen."

I have added to the list the following cases: Several Acanthaceae, for which see J. Scott in 'Journal of Botany' London new series volume 1 1872 page 161.

With respect to salvia see Dr. Ascherson in 'Botanische Zeitung' 1871 page 555.

For Oxybaphus and Nyctaginia see Asa Gray in 'American Naturalist' November 1873 page 692.

From Dr. Torrey's account of Hottonia inflata 'Bulletin of the Torrey Botanical Club' volume 2 June 1871, it is manifest that this plant produces true cleistogamic flowers.

For Pavonia see Bouche in 'Sitzungsberichte d. Gesellsch. Natur. Freunde'

October 20, 1874 page 90.

I have added Thelymitra, as from the account given by Mr. Fitzgerald in his magnificent work on 'Australian Orchids' it appears that the flowers of this plant in its native home never open, but they do not appear to be reduced in size. Nor is this the case with the flowers of certain species of Epidendron, Cattleya, etc. see second edition of my 'Fertilisation of Orchids' page 147, which without expanding produce capsules. It is therefore doubtful whether these Orchideae ought to have been included in the list. From what Duval-Jouve says about Cryptostachys in 'Bulletin of the Soc. Bot. de France' tome 10 1863 page 195, this plant appears to produce cleistogamic flowers.

the other additions to the list are noticed in my text.)

DICOTYLEDONS.

BORAGINEAE: Eritrichium.

CONVOLVULACEAE: Cuscuta.

SCROPHULARINEAE: Scrophularia.

Linaria.

Vandellia.

ACANTHACEAE: Cryphiacanthus.

Eranthemum.

Daedalacanthus.

Dipteracanthus.

Aechmanthera.

Ruellia.

l.a.b.i.aTAE: Lamium.

Salvia.

NYCTAGINEAE: Oxybaphus.

Nyctaginia.

ASCLEPIADAE: Stapelia.

CAMPANULACEAE: Specularia.

Campanula.

PRIMULACEAE: Hottonia.

COMPOSITAE: Anandria.

CRUCIFERAE: Heterocarpaea.

VIOLACEAE: Viola.

CISTINEAE: Helianthemum.

Lechea.

MALVEACEAE: Pavonia.

MALPIGHIACEAE: Gaudichaudia.

Aspicarpa.

Camarea.

Ja.n.u.sia.

POLYGALEAE: Polygala.

BALSAMINEAE: Impatiens.

GERANIACAEA: Oxalis.

LEGUMINOSAE: Ononis.

Parochaetus.

Chapmannia.

Stylosanthus.

Lespedeza.

Vicia.

Lathyrus.