C. J. Bond 349 



outside the central pistil and yet retain the five petals characteristic of the 

 female flower. (PI. XVI, fig. 6.) Although doubleness chiefly affects male 

 Begonia flowers, and is therefore a sex limited character, it is possible 

 under certain conditions, by cross pollination, to transfer this character 

 of doubleness to the female flower. Double female flowers so produced, 

 however, retain secondary male characters. The structure and arrange- 

 ment of the accessory floral parts are not influenced by being linked up 

 with maleness. In fact a primarily female flower with a well-formed ovary 

 and a central gynoecium may develop a complete ring of stamens and yet 

 retain the five petals characteristic of the female flower. (PI. XVI, fig. 6.) 

 From these facts we are I think justified in concluding that the presence 

 of male organs does not necessarily modify the secondary sex characters 

 of female flowers. The same is true of male flowers which develop 

 female organs. The secondary characters seem to depend on the 

 primary sex of the flower as shown by the central position of the 

 gynoecium or androecium on the floral axis. The accidental occurrence, 

 so to speak, of rudimentary, or even well developed, organs of the 

 opposite sex, does not affect the growth of the secondary sex characters. 

 That this should be so is not surprising when we recall the apparent 

 absence in plants of any secretion corresponding to the sex hormones 

 in animals. 



There is, however, evidence pointing to the existence of enzymes in 

 plants. 



Keeble (Plant Animals, 1910) suggests that the cambium cells 

 influence the neighbouring cortex cells and stimulate them to undergo 

 cell division by means of some secretory substance. He also suggests 

 that the green algal cells in Convoluta roscoffensis supjjly the bio- 

 chemical stimulus on which the later development of that organism 

 depends, and in the absence of which it fails to grow. 



There are also the important facts concerning the influence of fer- 

 tilization on the growth of accessory floral structures. Darwin showed 

 long ago that some kinds of foreign pollen can act as a poison to the 

 stigmata and pistils of certain flowers. The rapid wilting and the 

 falling within 36 hours of the petals of a successfully fertilized female 

 flower provides us with a practical indication as to whether the pollen 

 artificially introduced has " taken," and whether the flower is adequately/ 

 fertilized in any given case. But these latter examples are examples 

 of an inhibitory rather than a stimulatory influence. In the other 

 direction we have the stimulating eflect of the fertilized and growing 

 ovule on the tissues of the floral peduncle, and this influence is 



