Chap. Vir. POLYGAMOUS PLANTS. 285 



mote period, so that there will have been ample time 

 for some of the species to have been since rendered dioe- 

 cious. Asa Gray informs me that Coprosma is dioecious, 

 and that it is closely allied through Nertera to Mitch- 

 ella, which as we know is a heterostyled dimorphic 

 species. In the male iiowers of Coprosma the stamens 

 are exserted, and in the female flowers the stigmas; 

 so that, judging from the affinities of the above three 

 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 Eubia- 

 ceous genera) has been converted into the male Co- 

 prosma; and that an ancient long-styled form with short 

 stamens, small anthers and small pollen-grains has 

 been converted into the female form. But according 

 to Mr. Meehan,* Mitchella itself is dioecious in some 

 districts; for he says that one form has small sessile 

 anthers without a trace of pollen, the pistil being per- 

 fect ; while in another form the stamens are perfect and 

 the pistil rudimentary. He adds that plants may be 

 observed in the autumn bearing an abundant crop of 

 berries, and others without a single one. Should these 

 statements be confirmed, Mitchella will be proved 

 to be heterostyled in one district and dioecious in 

 another. 



Asperula is likewise a Eubiaeeous genus, and from 

 the published description of the two forms of A. sco- 

 paria, an inhabitant of Tasmania, I did not doubt that 

 it was heterostyled; but on examining some flowers 

 sent me by Dr. Hooker they proved to ' be dioecious. 

 The male flowers have large anthers and a very small 

 ovarium, surmounted by a mere vestige of a stigma 

 without any style; whilst the female flowers possess 

 a large ovarium, the anthers being rudimentary and 



* 'Proc. Acad, of Sciences of Philadelphia,' July 28, 1S6S, p. 183. 



