2 7 8 



GENERAL MORPHOLOGY OF PLANTS 



suspends the gamete cases. 



body. A cross wall now cuts off a body of protoplasm in the 

 end of each branch. This cell is the gamete case (gametangium) 

 and the protoplasm in each is a gamete (fig. 222). The remain- 

 ing part of each branch is a suspensor, so called because it 



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 be- 

 comes thick, black, and rough 

 with small wart-like protuber- 

 ances. This is the zygospore. 



419. 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. 



420. 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 

 colonies 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 growing side by side or mixed so that branches 

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



Fig. 223. 



Formation of zygospores in a mold 

 (Mucor mucedo) . A , two hyphse in contact, 

 end to end; 5, 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 Bref eld.) 



