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. 



loi. Tubercles of 

 leguminous plants. 

 — Dig up the roots of 

 any species of the pea 

 or bean family, and 

 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, through the hairs, and its 

 presence stimulates the formation of the tubercles. Seed- 

 7 



Fig. 70.— Transverse section of portion of 

 root of Listera. A, clumps of fungal hyphse 

 in cortical cells from which filaments pass out 

 into the soil through the root-hairs £ B. After 

 Chodat. 



