252 



GENERAL MORPHOLOGY OF PLANTS 



This cell is the gamete case (gametangium) and the protoplasm 

 in each is a gamete (fig. 211). The remaining part of each 

 branch is a suspensor, so called because it suspends the gamete 

 cases. The walls between the gametes dissolve so that there is a 

 mixing or fusion of the protoplasm of the two gametes. This 

 united body enlarges, and the wall becomes thick, black, 

 and rough with small wart-like protuberances. This is the 

 zygospore. 



406. Germination of the zygospore. The zygospore of the 

 bread mold has not yet been found to germinate, but that of 



a related mold (Mucor mucedo 

 Linn.) has. When it germinates 

 it produces at once a sporophore 

 and spore case containing numer- 

 ous asexual spores. These are 

 scattered and produce the my- 

 celium and successive cycles of 

 the asexual stage. 



407. The bread mold is 

 dioecious.* In the bread mold 

 (R. nigricans) the conjugating 

 branches always arise from dif- 

 ferent plants. The two branches 

 of an opposite sex nature, or 

 strain, never arise from the same 

 plant, that is from the mycelium 

 which came from a single spore. 

 There must be two different colo- 

 nies of mycelia, each from a single 

 spore of opposite sex natures, one 

 corresponding to the male and 





 one to the female. These tWO 



must be prowing Side by side Or 



mixed so that branches which 

 would be of opposite sex natures can meet and conjugate. Under 

 * Heterothullic, because there are two sorts of thalli, male and female. 



Fig> 2I2i 

 Formation of zygospores im a moid (Mucor 



mucedo >. A, two hypha; in contact, end to 

 end; B, the terminal'gametes; C, later stage, 

 the gametes fusing; D, a ripe zygospore; , 

 germination of a zygospore, the filament 

 forming a sporangium at once in this case. 



(After Brefeid.) 



