244 THE STRUCTURE OF FLOWERS. 



the more conspicuous the more masculine is the flower, 

 and the more attractive will it be — one with another, would 

 not therefore be so advantageous as crossing the moi-e female 

 plants with the conspicuous. The former, too, produce 

 relatively more offspring, and might tend to oust the others, 

 and reproduce both the "more masculine" and the "more 

 female " sorts. Intercrossing, therefore, coupled with en- 

 vironing conditions, may together bring about dioecism, as 

 in Strawberries. As this reasoning is rather dedticiive, it 

 must be only considered as a suggestion. 



Sexuality and Heterosttlism. — This undoubtedly is 

 another source of diclinism, as already alluded to. Mr. 

 Darwin alludes * to Coprosma and Ilitchella as indicating 

 this fact. " Coprosma is dioecious, and in the male flowers 

 the stamens are exserted, and in the female flowers the 

 stigmas i so that, judging from the affinities of these genera, 

 it seems probable that an ancient short-styled form, beaiing 

 long stamens with large anthers and large pollen-grains (as 

 in the case of several Rubiaceous genera), has been converted 

 into the male Coprosma; and that an ancient long-styled 

 form, with short stamens, small anthers, and small pollen- 

 grains, has been converted into the female form. According 

 to Mr. Meehan,t Miicliella repens is dioecious in some 

 districts : for he says that one form has small sessile anthers 

 without a trace of pollen, the pistil being perfect ; while in 

 another form the stamens are perfect and the pistil rudi- 

 mentary. MifcJieUa, therefore, would seem to be heterostyled 

 in one district and dioecious in another," and this can 

 scarcely be due to anything but environment. 



* Forms of Flowers, etc., p. 285. Sec also above, p. 228. 



t Proc. Acad, of Sci. of Philadelphia, July 28, 1868, p. 183. I do not 

 gather from Mr. Meehan's account that he found any difference as to 

 locality. Dioecism appears to be a constant character. 



