Chap. VH. POLYGAMOUS PLANTS. 285 



other family, and from their wide distribution we may 

 infer that many of them became heterostyled at a re- 

 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 flowers 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 Rubia- 

 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 

 perfect ; 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 Rubiaceous 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 



' Proc. Acad, of Sciences of Philadelphia,' July 28, ]86S,-p. 183. 



