52*1 MacDougal : Symbiosis and SArRoriivTiSM 



but no enlargements constituting sporangiolcs, vesicles or other 

 organs of interchange are to be seen. The cortex of the younger 

 portions of the coralloid structures is filled with starch granules 

 which are slowly corroded by the action of the developing hyphae. 

 Cells in which the hyphae have made many convolutions still 

 contain some starch, but it finally disappears. The hyphae in the 

 medio-cortex a distance from the tip arc yellowish and collapsed, 

 but no solid bodies are to be seen as a result of the liberation of 

 their disintegration products in the cortical cells. The proto- 

 plasm of the latter is well spent but normal, and the nuclei are 



I 



normal and active. The permanent mycelium sends out external 

 branches through the trichomes into the soil. The permanent 

 mycelium is, therefore, in the form of a sheathing cylinder with 

 numbers of branches opposite each other extending out into the 



^ 



substratum and into the cortex. It is to be pointed out in this con- 

 nection that the numerous statements to the effect that the fundus 

 gains access to the interior of the coralloid structure througli 

 the trichomes are obviously incorrect. Entrance to the ofTset in 

 the initial sta^e of the formation of the coralloid branches is per- 

 haps made in this way, but once inside the branch the permanent 

 mycelium is found which keeps jiace with growth of the cortex and 

 sends branches outwardly through the trichomes. The continued 

 and" repeated entrance of the fungus through the trichomes is an 

 assumption onl}^, ancf is based on the necessities of the theory of 

 mycorhizas as fungus traps rather than on the actual facts. 



The chcmotropic reactions of the fungus as shown by its metliod 

 of extension are of great interest. The permanent m^xelium tra- 

 verses the coralloid branches in the layer*? of cortical tissue first 

 differentiated. The tips of the h>'phal l^ranches arc attracted out 

 through the trichomes, presumably by atmospheric oxygen, or by 

 the humus products, which would increase ia concentration from 

 the base of the epidernial cells to the apices of the trichomes. The 

 attraction of the branches into the medio-cortical cells must be due 

 to a carbohydrate, rather than a nuclear product/ since it is quite 



4 



noticeable that all convolutions of the hyphae are made in regions 

 of the cell some distance from the nucleus. The tip of a hypha 

 may pass within its own diameter of the nucleus of the cortical 

 cell with mutual indifference, and only in a small number of in- 



