THE FUNGUS BODY OF HYPHAL ELEMENTS. 45 



young plant (as in the " damping off" disease in green- 

 houses), or it may develop slowly and not reach maturity 

 until the host is mature. 



53. Haustoria. — Those fungi which grow upon the sur- 

 faces of living plants (and those which grow in the internal 

 air-spaces) often have special branches for fastening them- 

 selves to the host or absorbing food from it. In the surface 



Fig. 53. — Epidermis and a few cortical cells of cowberry with mycelium of Calyp- 

 tospora occupying the intercellular spaces and pressing knob-like ends against the 

 cells from which a slender branch penetrates the wall and enlarges in the interior 

 into sac-like haustoria, d, b. a, club shaped hyphae which produce spore-mother- 

 cells, c, in the epidermis. Magnified 420 diam. — After R. Hartig. 



fungi these are usually very short, disk-like or lobed 

 branches which do not penetrate the cells of the host. In 

 other cases they are branches of minute diameter, which 

 enter the cells, and either enlarge into a knob (fig. 53) or 

 branch profusely (fig. 54). 



54. Fusion. — When the hyphae of a fungus grow very 

 close together, they frequently cohere and become so 

 changed in appearance as to lose all trace of resemblance to 

 filaments. Not only fusion but thickening and division 



