108 



COMPARATIVE MORPHOLOGY OF FUNGI 



Peronospora are just as important as the sporangia of Plasmopara. In 

 the Mucoraceous series, the primary import does not lie in an inhibition 

 of formation of spores whose individuality is retained but in a degenera- 

 tion of sporangia. A decrease in size of the sporangia leads to a decrease 

 in the number of spores. Biologically, the result is the same in both 

 cases: a single conidium replaces sporangia with many spores. 



Besides this asexual reproduction, in most Mucoraceae sexual organs 

 are known. In the homothallic forms their appearance is mainly depend- 



Fig. 66. — Mucor Mucedo. Zygospore formation. 1. Two copulation branches 

 approach. 2. Separation of gametangia, a, from suspensors, b. 3. Formation of azygo- 

 spores instead of copulation. 4. Mature zygospore, b, between the suspensors, a. 5. 

 Germination of zygospore. (1 to 4 X 225; 5 X 60 after Brcfeld.) Mucor erectus. 6, 7. 

 Azygospore formation. Mucor tenuis. 8, 9. Azygospores. (After Bainier.) 



ent on conditions of nourishment; the heterothallic forms require the 

 presence of both sexes. Mycelia of one sex may be cultivated alone for 

 any number of "generations" without the appearance of normal sexual 

 organs, which appear promptly whenever the opposite sex is brought 

 into the vicinity. 



If two sexually mature (in heterothallic forms also dynamically 

 opposite) hyphae come in contact with one another under favorable 

 conditions, each forms an outgrowth toward the other (Fig. 66, 1). This 

 is cut off from the sporiferous hyphae close behind the tip by a diaphragm- 

 like wall laid down from the edge inwards (Fig. 66, 2). The tip cell is 



