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 more 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 deductive^ it 

 must be only considered as a suggestion. 



Sexuality axd Heterostylism. — This undoubtedly is 

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

 Darwin alludes * to Coprosma and Mitchella as indicating 

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

 the stamens are exserted, and in the female flowers the 

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

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

 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 Mitchella repens is dioecious in some 

 districts t 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. Mitchella, 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. See 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. 



