124 



Notwithstandiii",' llu- wide (li>lrilinti(in, tlii' s])ceics sei'iii tn liavc a rt'iiiarkalily 

 "similar habitat, ami fonseqiieiitly the plants show a very striking reseml)iaiice in 

 regard to their striieture and adaptation to their rather peculiar surroundings. 

 The plants of the genus are all found in low, (iainji places, with an extreme 

 reached in P. ophioglosHoides, which grows in sphagnum bogs througliout Nortli 

 America, Jajjan and Europe. With reference to the other North American 

 S])ecies of Pogonia no marked variation from tlie regular terrestrial orchids has 

 been observed which would indicate that the plants had undergone any special or 

 irregular variations as a result of their peculiar environments. 



In an examination (tf the roots of P. npltioglossoiden it was found that a 

 striking exception existed which might be a very suggestive one when considered 

 from the standpoint of tlu' adaptation of the plant in order to better fit it to with- 

 stand the jieculiar difficulties of its surroundings. 



The roots of all phanerogams arc provided at the tip with a series of initial 

 groups, from which diflf'erentiate the various parts of the root in the following 

 ■order : From the calyptrogen comes the root caj), from the dermatogen the 

 •ei)idermis, from the periblem the cortex, and from the plerom the central 

 cylinder. Sometimes one or more of these grou[)s are combined and this is the 

 condition ascribed by Trent to the orchidaceu', regarding which he hoJds that the 

 calyptrogen is not present and the root cap and ej)idermis originate from a com- 

 mon initial grou]), the deimatogcn. Janczewski holds that in these monocots we 

 find a well marked calyptrogen, and in this he is supjiorted by Flahault and others. 



AVith reference to this arrangement, in the roots of P. ophioylotnioides, was 

 found what is belit'ved to l)e a marked exception to all phanerogams, except 

 pos.sil)ly a few i)ar,isitic ones. 



The roots of the plant arc small, very long, much branched, and provided 

 with a few root-hairs. At the tij) we find an entire absence of a root-caji, and the 

 cells of the dermatogen, with but slightly thickened walls, form the outside cov- 

 ering, which in the growing jjlant is quite green. 



The cells of the dermatogen undergo a periclinal extension 2-8 mm. back 

 from the ti{), and at this point they (piickly change into the more firm, brown epi- 

 dermis which soon shows the differentiation of the root hairs. The dermatogen 

 •cells are very large, regular and with conspicuous nuclei showing great activity. 



Another condition not seen in other roots is the very rapid development of 

 the fibro-vascular bundles from the procambium which usually extends some 

 distance back from the tip, and from it very gradually difTerentiate the elements 

 •of the fil)ro-vasctilar system, whereas in Pogonia ophioglon^ioideii, the xylem shows 

 reticulated tracheids often not more than ten cells back from tln' initial group of 



