T. Holm — North American Terrestrial Orchidece. 211 



"tuberous body" may from a morphological viewpoint be 

 justifiable, when we compare the rhizome, and especially the 

 arrangement of the roots, with that of other terrestrial Orchi- 

 dece in which all the roots are free, slender and with only one 

 central-cylinder. In Arethusa, for instance, the disposition 

 of the roots is such that if they were united or grown together, 

 they would exhibit exactly the same structure as we have 

 shown being the characteristic of the lower portion of the 

 " tuber " in the Ophrydece. But the habit of these plants is 

 too distinct to allow us even to imagine ourselves, that such 

 union of the roots in Arethusa might be possible. 



Summary. 



1. A velamen and exodermis is developed in the terrestrial 

 Tipularia discolor and Bletia verecunda. 



2. Some cells of the cortical parenchyma in Ziparis liliifolia 

 show the same spiral thickening as is known from the epiphytic 

 genera. 



3. A similar spiral thickening was observed in the epidermis 

 and hypoderm of several species of Spiranthes. 



4. The pericambium is composed of two layers in Bletia 

 verecunda. 



5. The pericambium was observed to be continuous in a 

 number of species pertaining to different genera. 



6. The pericambium was observed to be continuous or inter- 

 rupted in the same root of Orchis, Pogonia verticillata, vari- 

 ous species of Spiranthes, etc. 



7. Sphserocrystals abound in the inner parenchyma of 

 several species of Platanthera. 



8. All the roots of JEpidendrew, JVeottiece and Cypripediece 

 examined possess only one central-cylinder. 



9. A true pith and, sometimes, of quite considerable width 

 was observed in Tipulai^ia, Arethusa, Calypso, Spiranthes, 

 Chlorcea, Goodyera, Habenaria, Aplectrum, Bletia, Ziparis, 

 Calopogon and Cypripedium Califomicum. 



10. The cortical parenchyma is traversed by wide lacunes 

 and by a special duct in Habenaria repens. 



11. The upper portion of the so-called " tuber " of the 

 Ophrydem examined consists of elements pertaining to a stolon, 

 a bud and some roots ; the lower part, on the contrary, of 

 roots alone. 



12. The roots of our terrestrial Orchidece very often repre- 

 sent mycorhizoe, but not all the roots of the same species, nor 

 of the same specimen. 



Brookland, D. C, May, 1904. 



