Nutrition. 



97 



and note the manner in which the fine hyphal threads of 

 the parasite penetrate the cells of the host, or show de- 

 vices for drawing nutritive material from them. Rusts, 

 mildews, and molds will offer many accessible examples for 

 such studies. 



100. Symbiosis of a seed plant and a fungus. Cut 

 sections of the apical 



portions of the roots 

 of any coniferous tree, 

 and note the presence 

 of a fungus which may 

 enwrap the root in some 

 species, replacing the 

 piliferous layer, while 

 in others it penetrates 

 the cortical cells, send- 

 ing hyphae out into the 

 substratum either 

 through the root-hairs 

 or through the walls of 

 the epidermal cells. 



101. Tubercles of 



legUminOUS plants. F}g< 70 ._ Tr ansverse section of portion of 



Dig Up the rOOtS Of root of Listera. A, clumps of fungal hyphse 



- , in cortical cells from which filaments pass out 



any species me pea into the soil t h rou gh the root-hairs B B. After 



or bean family, and Chodat. 

 observe characters of 



nodules, or tubercles. Make careful anatomical examination 

 of the tubercles, and cut thin sections with a razor. Numbers 

 of globular or ovoid organisms will be found in the paren- 

 chymatous tissues. Stain with iodine, and ascertain nature 

 of other substances present. The bacterial organism enters a 

 young root in a filamentous form, t through the hairs, and its 

 presence stimulates the formation of the tubercles. Seed- 

 7 



