526 MacDougal : Symbiosis and Saprophytism 



ings. The lo to 15 layers of cortical tissues are furnished with 

 very large intercellular spaces, which may denote an epidermal 

 transpiration of some importance, though no special adaptation for 

 this purpose could be detected. Crystal cells are scattered through- 

 out the cortex and appear even in the epidermis. The pericycle 

 is composed of several layers of elongated cells with thickened 

 walls and yellowish brown contents. The bundles are scattered 

 in the stele with the xylem and phloem radially arranged. Then' 

 degeneration is fairly uniform with that of the rhizome and its 

 branches. The leaves are sheathing, destitute of stomata, and 

 show no differentiation of tissue for food-formation, or transpira- 

 tion, except that the globular parenchyma shows great intercellu- 

 lar spaces. As noted above they are free from chlorophyll 

 C. Arizonica differs from C. Corallorhiza (C. innnta) in the formation 

 of a bulky premorse rhizome furnished with stomata, the total lack 

 of chlorophyll in the shoot, with absence of stomata, and in the 

 greater degeneration of the stele. The differentiation of the fungal 

 symbiont into a permanent mycelium with short-lived and external 

 and internal branches seems to be a mycorhizal character described 

 here for the first time, though it is present in C. Corallorliiza and 

 other species. The hyphae in the coralloid formation of C. Co- 

 rallorldza, C. uiultiflora and others are applied to the nuclei in the 

 cortical cell while in C. Arizonica this is not the case, indicating a 

 difference of chemotropic reaction of the fungus in the two in- 

 stances. 



Relations of the mycorhizal components 



The fungus in the coralloid formations of CorallorJiiza draws its 

 nourishment from two sources ; .from the humus products of the 

 soil and from the carbohydrates in the cortex. The material thus 

 obtained is used in the construction of extensions of the mycelium 

 and its branches. With the growth and progression of the my- 

 corhiza, the older internal branches of the mycelium which have 

 formed dense masses in the medio-cortex undergo disintegration 

 and the products thus liberated may be drawn in two directions : 

 toward the apex of the mycorhiza and toward the premorse rhi- 

 zome. On arrival at both places the surplus matei'ial is converted 

 into starch. The starch of the rhizome is used in the construe- 



