136 HETEKOSTYLED DIMORPHIC PLANTS. Chap. UI. 



in the United States. Lastly, from Mr. W. W. Bailey's 

 description,* it appears that the Mexican Bouvardia le- 

 iantha is heterostyled. 



Altogether we now know of 17 heterostyled genera 

 in the great family of the Rubiacess; though more 

 information is necessary with respect to some of them, 

 more especially those mentioned in the last para- 

 graph, before we can feel absolutely safe. In the 

 ' Genera Plantarum,' by Pentham and Hooker, the 

 Rubiacese are divided into 25 tribes, containing 337 

 genera; and it deserves notice that the genera now 

 known to be heterostyled are not grouped in one or 

 two of these tribes, but are distributed in no less than 

 eight of them. From this fact we may infer that 

 most of the genera have acquired their heterostyled 

 structure independently of one another; that isj, they 

 have not inherited this structure from some oj:e or 

 even two or three progenitors in common. It further 

 deserves notice that in the homostyled genera, as I 

 am informed by Professor Asa Gray, the stamens are 

 either exserted or are included within the tube of the 

 corolla, in a nearly constant manner; so that this char- 

 acter, which is not even of specific value in the hetero- 

 styled species, is often of generic value in other mem- 

 bers of the family. 



» 'Bull, of the Torrey Bot. dub,' 1876, p. 106. 



