444 



COMPARATIVE MORPHOLOGY OF FUNGI 



rhizomorphs become several millimeters thick, terete, white, tough and 

 flexible when young, gray to black and brittle in age. They consist 

 of a ground tissue of thin-walled vegetative hyphae in which are imbedded 

 a number of functionally specialized hyphae (fibrous, vascular, etc., Fig. 

 268). These enable the fungus to penetrate unfavorable regions, such 

 as cracks in the walls, and thus reach fresh uninfected wood to continue 



Fig. 286. — Merulius lacrymans. Fructifications on rotting beam. (Natural size; after 



Falck, 1912.) 



their growth. Upon lack of nourishment, the protoplasm contracts 

 into short sections, surrounds itself with a thick wall and produces 

 gemmae. 



The next stage is reached by the reflexed forms, such as M. tremellosus 

 which has a broad gelatinous subhymenial layer. The highest stage 

 is reached in the dimidiate forms, which in M. rubellus form groups of 



