204 T. Holm — North American Terrestrial Orchidece. 



istic spiral or simply striate thickening of the cell- walls ; other- 

 wise the structure is identical. There, is, furthermore, an 

 exodermis of exactly the same structure as we know from the 

 epiphytic genera. The cortical parenchyma is thin-walled and 

 consists of about 8 layers of roundish cells with narrow inter- 

 cellular spaces ; many hyphae, but no starch, was observed in 

 this tissue. The endodermis and the continuous pericambium 

 are both thin-walled and surround 5 short rays of hadrome, 

 alternating with 5 small groups of leptome ; a pith occupies 

 the inner portion of the central-cylinder. 



JBletia verecanda Sw. 



In several respects the root-structure of Bletia agrees with 

 that of Tipularia, but some, and indeed quite important, 

 deviations were noticed. These consist in the more typical 

 development of velamen, the cell-walls of which exhibit the 

 characteristic tine and spiral thickening peculiar to this tissue ; 

 moreover by the presence of a double pericambium, which is 

 moderately thickened and to the same extent as the hadrome, 

 thus the position of the proto-hadrome vessels in proportion to 

 the pericambium could not be made out satisfactorily. The 

 hadrome forms 8 short and broad rays alternating with large, 

 roundish groups of leptome, inside of which there is a large, 

 thin- walled pith with intercellular spaces of quite considerable 

 width. 



These roots, described above, belong to the first type, all 

 being relatively slender and possessing only one, central -cylin- 

 der. In several respects they agree with the second type, in 

 which, however, the dimensions of the roots have increased to 

 such an extent as to deserve the term " tuberous " on account 

 of the much broader zones of the cortex and pith, besides by 

 the larger number of rays or better u groups " of hadrome and 

 leptome. 



Type B. 



Spiranthes gracilis Big., S. simplex Gray, S. prmcox Wats., S. 

 Homanzoffiana Cham., S. cernua Rich., S. cinnabarina 

 Hemsl. and S. Asagrcei Schaff. 



Even when the roots are quite numerous, as in the last two 

 species, they, nevertheless, retain the same swollen aspect as 

 when they are but few in number or single, as in S. simplex. 

 The internal structure is, also, very uniform in these species, 

 and not very different from those described above, but per- 

 taining to other genera. 



Common to these species of Spiranthes is a thin-walled epi- 

 dermis with many hairs, besides a hypoderm of one layer, the 

 cells of which are smaller than those of the adjoining cortex. 



