, Sporangia 



Formation*^ 

 of zygote 



O O' _ 



Germinating 

 spores ^ 



igj/ 



Kyphae / 



Penicillium 



1 



[ V 



SPORES IN COMMON MOLDS 



Absorbing 



hyphae 



Spores are generally formed by the repeated division of protoplasm. In the black 

 mold, spores are formed in an enlarging cell at the tip of a vertical thread; this re- 

 sults in a capsule, which breaks and lets the spores scatter. In the blue mold, spores 

 are separated off from the terminal branches of threads. In the black mold two 

 threads sometimes meet, so that the protoplasm combines into a sporelike cell called 

 a zygospore 



of the cells passes over into the opposite cell; the two masses of protoplasm 

 unite and form a new kind of cell (see illustration opposite). 



Like a spore, this new cell (which forms a thick, dark cell-wall) is able to 

 start a new growth after waiting indefinitely through unfavorable conditions. 

 But it is unHke a spore in its origin, for it arises from the conjugation, or unit- 

 ing, of two pre-existing cells. The cells that take part in the conjugation are 

 called gametes, from a Greek word meaning "to marry"^ — that is, to join, or 

 unite. The cell that results from the conjugation is called a zygospore — that 

 is, a spore formed by a yoking, or joining together. It is sometimes called a 

 zygote for short. 



The common molds are widely distributed by the millions of spores which 

 they produce by the successive division of the protoplasm. In addition, 

 zygotes are produced in black mold by the fusion of protoplasm from two 

 different hyphae (see illustration above). There are distinct strains in the 

 species, and conjugation can take place only if threads of two different strains 

 come together. There are no doubt chemical differences between the two 

 strains of mold, but what the differences are has not yet been found out. 



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