ORCHIDACEiE 



I. Column denticulate or paucidentate at the apex. Anther de- 

 cumbent with the loculi facing downward. Pollen grains 

 simple or compound with the extine free from pits or reti- 

 culations. 



A. Pollen grains simple, not cohering in tetrads Pogonia 



A. Pollen grains compound, cohering in tetrads. 



a. Leaves solitary or alternate Cleistes 



a. Leaves (5 or 6) verticillate Isotria 



IL Column entire at the apex or simply lobed. Anther erect, with 

 the loculi facing outward. Pollen grains compound with 

 the extine pitted or reticulated. 



A. Anther rigidly attached to the top of the column Triphora 



A. Anther mobile at the top of the column and articulated 



with it Psilochilus 



A glance at the key reveals a very important point, namely, that 

 Triphora is set apart, not only by means of an easily determined 

 character found in the pollinia, but by a peculiar structure of the 

 column that does not occur in any of its allies. This character, in 

 my estimation, is indicative of deep-seated differences which are 

 accentuated when we examine the vegetative structure of the 

 plants. 



The subterranean organs of the four genera that occur within 

 our range offer some very interesting differences. I believe these 

 were first noticed in detail by Theo. Holm in his paper already 

 referred to. Aside from fundamental differences, the gross vege- 

 tative characters offer a means for dividing the alliance under 

 consideration into two groups ; Triphora possessing a most re- 

 markable system of underground tubers and stolons which will 

 receive attention on another page, Pogonia, Cleistes and Isotria 

 propagating by means of root-shoots or successive buds, never by 

 true stolons. I am unable to include Isotria affinis as a plant that 

 propagates vegetatively by root-shoots, as this species is so rare 

 that material is difficult to obtain in sufficient completeness to 

 warrant conclusions regarding its vegetative system. The most 



