:hap. V] 



THE SOIL 



109 



jranulatus, and Noack also in species of Geaster, Agaricus, Lactaiius and 

 Tortinarius. and in the well-known Agaricus muscarius, the inj'corhizal fungi 

 )f our forest trees. 



The relations between fungus and root are symbiotic, that is to say, 

 iseful to both organisms, at least in the case of endophytic fungi, for 

 .'. Groom's observations on Thismia lead to the conclusion that the pre- 

 sence of the fungus promotes the elaboration of proteids in the root-cells, 

 ind that between both organisms an exchange of nutritive matter occurs, 

 ilthough the nature of this is unknown. 



The relations between fungus and root are very simple in epitrophic mycorhizae ; 

 n those that are endotrophic, on the contrary, they are often very complicated. As 

 n instance of the latter, the mycorhiza of Thismia Aseroe, which has been studied in 

 letail by P. Groom, may be described somewhat more minutely (Fig. 59). The 



Fig. 56. Monotropa Hypopitys. Portion of a 

 young plant. After Kamienski. 



Fig. 57. Monotropa Hypopitys. Epi- 

 dermis and mycoihiza-fungus. Magnified 

 450. After Kamienski. 



oral-like branching root-system has a fine papillose surface. The thin-walled 

 eripheral tissues free from starch, which the author termed the sheath (s/i.), are 

 aversed longitudinally by a few fine inj'celial hj'phae. Within the sheath next 

 ccurs a sharply differentiated laj'er of cells (e.c), all of which contain swollen 

 yphae, wound round in a kind of coil. These hyphae are externally coated with 

 ytoplasm. Inside the exocortex (e.c.) comes the limiting layer (/./.), in the cells 

 " which fine, delicate hj'phae here and there dilate into thick vesicles filled with 

 roteids. An inner part of the cortex (mediocortex iii.c.) is composed of two or 

 iree layers rich in starch and characterized by possessing dead, j'ellow masses of 

 lycelium in all its cells, except those containing raphides. The endodermis and 

 mtral cylinder are free from the fungus. 



On entering from the sheath into the deeper lying cells the terminal point of the 

 ycelial thread grows directly towards the nucleus. In the medullary layer of 

 le cortex (mediocortex), where the relations are clearest, the starch of the infected 

 :11s is at once dissolved, but reappears on the death of the fungus. The latter 



