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A TEXTBOOK OF BOTANY 



[On. X 



spores in round sporangia raised on tall, vertical stalks, 

 whence they are strewn by the wind ; and it is these dark- 

 colored sporangia which form the distinctive black spots 

 of the bread mold (Fig. 304). The sexual reproduction, 

 which occurs rarely, is zygosporic. Short, blunt branches 



FIG. 304. The Bread Mold, Rhizopus nigricans. 



Upper left, mycelium and sporangia ; X 30 ; next a sporangium in section, 

 X 160. Right, series of stages in the development of a zygospore, X 160. 

 Left, mycelium germinating, X 160, and spores, X 650. 



develop towards one another from adjacent hyphse, come 

 together end to end, and unite ; the contents of their tips, 

 cut off by cross walls, merge into thick-walled resting spores 

 which later germinate to new mycelia. In some Molds 

 it has been found that not any mycelium will thus unite 

 with any other, but only certain ones with certain others, in 

 ways to imply the existence of a physiological differentiation 



