ORCHIDACE^ 



ent lip-base. Isotria and Cleistes, characterized in part by the 

 unpitted extine of the pollen, remain. They are separated from 

 each other by means of the foliage, Isotria having five or six 

 leaves disposed in verticils, while in Cleistes the leaves are soli- 

 tary or alternate. The verticils of leaves in Isotria are of extraor- 

 dinary interest as they indicate a line of development, that now 

 lacks a parallel in the Orchidaceae, the nearest approach to it 

 being found in the Antarctic Codonorchis. It is when we con- 

 sider the significance of verticillate leaves in the evolution of 

 the orchids that this peculiarity in Isotria assumes deep signifi- 

 cance in attempts at generic segregation. 



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