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BOTANY: PRINCIPLES AND PROBLEMS 



1. Mucorales, the True Molds or Black Molds (Fig. 164).— 

 These fungi are very common on moist, decaying organic material 

 such as manure, rotting fruit, and the hke. Their white, cob- 

 webby mycehum, composed of much-branched hyphae, freely 

 penetrates the substratum in all directions. From the surface, 

 stout hyphae arise into the air and bear at their tips globular 



Fig. 165. — Mucor. Formation and germination of the zygospore. A, two 

 conjugating hyphae in contact. B, a gamete, a, has been cut off from the end of 

 each hypha. C, the enlarged gametes. D, thick-walled zygospore which has 

 arisen from a union of the two gametes. E, zygospore germinating to form a 

 sporangium. {From Slrasburger, after Brefeld). 



sporangia which burst and liberate masses of dark-colored 

 spores, each of which may germinate directly into a new plant. 

 Sexual reproduction is isogamous or essentially so (Fig. 165). 

 Two short branches or suspensors, arising from adjacent hyphae, 

 approach one another and come into contact end-to-end. From 

 the tip of each is cut off a single multinucleate cell which is the 

 gamete, and these two adjacent gametes fuse to produce a thick- 

 walled zygospore. It has been found that two distinct sexual 

 strains often exist, entirely similar outwardly but functioning 

 quite differently in reproduction. These have been called the 

 plus and the minus strains and correspond to the two sexes, for 



