392 AUTOGAMY. 



tinguished a series of very wonderful forms. A common characteristic of them all 

 is the stunted development or complete abortion of petals which would otherwise 

 attract insects by their scent, colour, or honey. The only function of the petals is that 

 of an envelope under cover of which ovules and stigmas, anthers and pollen, attain 

 maturity and are able to enter into combination with one another. In many cases 

 there is no trace of a corolla to be seen; green sepals alone are developed into a 

 floral envelope, and they are kept fast closed and cover the stamens and pistil in 

 the form of a hollow cone. Thus, for instance, Aremonia agrimonioides, a plant 

 growing abundantly in the forests of Carniola, has cleistogamous flowers about a 

 millimetre in diameter, in which stamens and sepals spring from the edge of the 

 excavated disc, whilst petals are entirely absent. In other cases, though petals 

 exist, they remain small and of a greenish-white tint. Precisely those parts of the 

 corolla which in open flowers are most conspicuous in form and coloration are here 

 abortive. Thus, in the cleistogamous flowers of several species of Violet, the 

 spurred petal, which in the open flower is the most striking, is scarcely recognizable; 

 its lamina is oval in outline, and is rolled into a hollow cone covering tlie anthers 

 and stigma. The anthers in most cleistogamous flowers are so situated that when 

 the pollen is ripe and issues from the loculi it comes immediately into contact with 

 the stigma. Sometimes, it is true, there is a tiny interval between the pollen 

 adherent to the anther-lobes and the stigma, but in that case tubes are put forth by 

 the pollen-cells in the direction of the stigma, and these tubes lay themselves upon 

 the papillae on the stigmatic surface and thence pursue their way to the ovules. In 

 the cleistogamous flowers of the Henbit Dead-nettle {Lamium amplexicaule) it has 

 even been observed that the anthers do not open, but that, nevertheless, pollen-tubes 

 emerge from the pollen-cells, perforate the walls of the anther and grow in the 

 direction of the stigma until they reach it. If a cleistogamous flower of this kind 

 is examined after autogamy has been accomplished within it, one might at first 

 sight think the anthers and stigmas were adnata to one another, so firm is the union 

 of the pollen-tubes with the stigma. 



As has been already said, all species of plants which produce cleistogamous 

 flowers also develop other open ones. For the most part these latter possess very 

 striking forms, scents, and colours, and are adapted to receive the visits of insects 

 and to undergo cross-fertilization through their agency. It is interesting to note, 

 however, that these open flowers possess none of the contrivances for effecting 

 autogamy in the event of a dearth of insects. From these observations we are 

 justified in supposing that we have here a sort of division of labour, inasmuch as 

 the functions, usually discharged by one form of hermaphrodite flower alone, are 

 here divided between two kinds of flower — both also hermaphrodite — viz., cross- 

 fertilization is assigned to those that open, self-fertilization to those that remain 

 closed. 



Amongst Grasses, Rushes, Scirpuses, and other plants of the kind, which produce 

 dust-like pollen in their hermaphrodite flowers, only a few species are known to 

 possess cleistogamous flowers. The oldest established example is that of Oryza 



