48 



COMPARATIVE MORPHOLOGY OF FUNGI 



they come to rest on the young leaves, make a few amoeboid movements 

 and put a short rhizoid into the epidermis. The zoospore body develops 

 shortly into an irregularly indented sporangium, sessile as in Rhizo- 

 phidium. At maturity its content breaks up into numerous zoospores. 

 A part of the walls swells, bursts open and liberates the zoospores. Under 

 favorable conditions, a new sporangium may grow five or six times from 

 the rhizoid into the emptied sheath. 



In the formation of hypnospores the content of the zoospores pass 

 over into the rhizoid, which swells up at its end into a small cell. When 

 this is mature, a smaller basal cell is abjointed on the side next the empty 



SW3, 









f* 



Fig. 32. — Physoderma Zeae-maydis. 1. Hyphae with turbinate cells. 2. Mature 

 zoosporangium discharging zoospores by the removal of a lid. 3. Mature zoospore. 4, 

 Amoeboid zoospore. 5. Hyphae with young, binucleate hypnospores. (After Tisdale, 

 1919.) 



zoospore membrane. The larger, rich in oil droplets and reserves, is 

 divided into two or more daughter cells; these develop to hyphae which 

 penetrate to neighboring cells of the host and there form similar swellings. 

 On these swellings resting sporangia are formed in a manner as yet 

 unknown. 



In Physoderma Zeae-maydis which, in North America, causes a disease 

 of maize and teosinte, the hypnospores are liberated as a brown powder 

 in the spring by the rupture of the epidermis of rotting leaves. Their 

 optimum of germination is very high, 26 to 28°. At germination a por- 

 tion of the exospore is raised like a lid (Fig. 32, 2), the endospore bulges 

 out, finally ruptures and liberates 20 to 50 uniflagellate zoospores. These 

 swim about 1 to 2 hours, come to rest, form amoeboid processes (Fig. 

 32, 4), surround themselves with a membrane and put forth into the 



