78 



MANUAL OF BOTANY 



Fia. 830. 



number of spores or gonidia. The wall of the gonidangium 

 usually becomes impregnated with crystals of oxalate of calcium. 

 The sexual reproduction is carried out by means of undifferen- 

 tiated gametes. Two hyphse from the vegetative part of the 

 mycelium approach each other, and a septum cuts off from each 

 a small cell, which is the gametangium. The two gametangia 

 come into contact, and the waUs between them are absorbed, so 



that the gametes, which are the 

 undifferentiated protoplasm of 

 the gametangia, fuse together, 

 forming a zygospore (fig. 830). 

 This grows into a globular body 

 which secretes round itself a 

 thick cuticularised wall. After 

 a period of rest this body ger- 

 minates, pulling out a small 

 mycelium, called a, promycelium, 

 which gives rise to a sporangium 

 (fig. 830, sj)) much like that 

 borne upon the ordinary fungus 

 body. This promycelium repre- 

 sents the sporophyte, the ordi- 

 nary form being the gameto- 

 phyte. In some species of Mucor 

 the gametangia are single and 

 conjugation does not take place ; 

 the body produced partheno- 

 genetioally by such a gametan- 

 gium is called an azygospore. 



Under unfavourable condi- 

 tions of nutrition, as when the 

 hyphsE are immersed in liquid, 

 the mycelium of Mucor may 

 divide up into a number of 

 oidium-like cells much like yeast 

 cells. This is called the Torula 

 form ; it is capable, like yeast, 

 of setting up alcoholic fermentation in a sugary fluid. Sonae- 

 times the separate cells are large and thick-walled, when they 

 are linown as Chlamydospores. 



There are two other groups in this sub-class, the Chytridiaceas 

 and the Entomophthoraces. The former produce zoospores in 

 ordinary sporangia or gonidangia, and in special thick-walled 



^/? 



Fig. 830. Conjngatiou iu Mucor 

 Mucedo. h. Twu hyphse which have 

 come into contact at their apices, 

 aud eacli lias cut off from itself a 

 cell. zyg. Zygospore resulticg from 

 the fusion of these cells, ziff/^. Adult 

 zygospore after germination, p. 

 Promycelium bearing a sporan- 

 gium, syj. 



