246 NUTRITIVE METABOLISM 



food for Penicillium, and that the solution of mineral salts alone 



is not sufficient. Many other organic substances may be tested 



in this same manner. 



314. Mycorhizas : Associations of Higher Plants and Saprophytic 



Fungi. Take up a mass of the finer roots of beech, oak, or 

 any coniferous tree and carefully wash away the 

 adherent soil. Note the club-shaped branches of 

 the smaller roots, constituting mycorhizas. Cut 

 cross and longitudinal sections of the structures, 

 and note the position and development of the fungus 

 which may form a layer of hyphae around the. root 

 replacing the root hairs. The fungi may occupy 

 the external layers of the root, or may live in the 

 cortical tissues sending branches of the hyphae out 

 through root hairs in other instances. Make mi- 

 crochemical tests, and ascertain the nature of bodies- 

 found in the hyphae, or their enlargements, and the 

 substances in the bodies of the higher plants used 

 as food by the fungi. The types which will come 

 under observation in this manner are examples in 

 which the higher plant receives only a small pro- 

 portion of its nourishment from the associated fun- 

 gus. Many seed plants have developed this habit 

 so strongly that they receive almost all of their food 

 material from the fungus, and carry on transforma- 



, tions with the material received, of which the lower 



Fig. 123. Co- ' 



rallorhim odon- P lant ls incapable, and yield the product to the 

 torrhiza with fungus. It will be profitable to examine two ex- 

 coralloid mycor- amp i es f this type, of which Monotropa has en- 

 from subterran- ^rely lost its chlorophyl, and Corallorhiza which re- 

 ean branches, tains a small amount, and is presumably able to 

 carry on more or less photosynthesis. 



Obtain clumps of Monotropa from the woods^ in the autumn 

 and carefully separate the roots from the adherent humus. Cut 

 sections and ascertain the anatomical relations of the two plants. 



