106 THE FUNGI WHICH CAUSE PLANT DISEASE 



during malting. It is distinctly a wound parasite and is unable 

 to force entrance through a sound epidermis. 



The richly branched mycelium which varies from very thin and 

 hyaline to thick, coarse and slightly fuscous, is found throughout 

 the rotten portion of the host. After a period of luxuriant vegeta- 

 tive growth hyphse protrude to the air, first through existing 

 ruptures in the epidermis, later by rifts forced by the fungus 

 itself. Sporangiophores then form in dense bush-like growths, 

 each sporangiophore bearing one terminal sporangium. The 

 sporangia are at first white, later black and contain very numerous 

 spores. Spore formation has been closely studied by Swingle.^^® 

 Aerial stolon-like hyphae reach out in various directions and at 

 their points of contact with some sohd develop holdfasts (Fig. 72) 

 and a new cluster of sporangiophores. 



Zygotes are produced by union of two myceUal tips as is shown 

 in Fig. 70. 



Orton ^^* inoculated pure cultures of this fungus on sterile raw 

 Irish potato and induced typical decay. He also noted that there 

 was a difference in the rate of decay produced by strains of Rhizo- 

 pus derived from different sources and that the most rapid decay 

 of potatoes was caused by strains taken from rotting potatoes. 



R. necans Mas.^^' causes decay of lily bulbs in Japan. 



R. schizans Mas. is cited as the cause of split-stone in peach. ^^ 



Mucor Linnaeus (p. 104) 



Mycelium all of one kind, buried in the substratum or grow- 

 ing over its surface; sporangiophores scattered or not, simple 

 or branched; sporangia globose; columella cylindric, pyriform or 

 clavate; spores numerous, variable; zygospores globose, smooth or 

 warty. 



Some thirty species, chiefly saprophytes. 



M. mucedo L. is destructive to beech nuts in winter. 



M. pyriformis Fisch and M. racemosus Fes. cause decay of 

 fruits. 



Choanephoraceae (p. 103) 

 MyceUum parasitic on living plants; sporangia of two kinds; 

 macrosporangia globose, columella small, spiny, spores few, on 



