MORPHOLOGY OF THE MOLDS 53 



Sexual Reproduction in Molds. — Molds having nonsep- 

 tate mycelium produce a type of sexual spore termed a 

 zygospore. Those molds with septate mycelium, which pro- 

 duce sexual spores, develop ascospores. 



The process of zygospore formation can most readily be 

 understood by reference to the accompanying figure. Two 

 filaments lying near each other send out branches which 

 approach each other and finally touch. The cell walls sepa- 

 rating the two tips are absorbed, resulting in union of 

 the protoplasm of the two cells. Cell walls are then 

 formed, separating the fused mass of protoplasm from the 

 parent hyphae. The nuclei of the two masses of proto- 



Fig. 34. — Development of a zygospore in a mucor. 



plasm apparently fuse in pairs. The resultant spore or 

 cell enlarges markedly in size, develops a very thick, usually 

 brownish cell wall, frequently marked by spines or by 

 irregular thickenings. Under favorable conditions this 

 zygospore germinates and develops a new mold. 



The development of ascospores is somewhat more complex 

 than that of zygospores. Two cells, frequently of some- 

 what different size and shape, develop from the same or 

 adjoining threads. The cells coil together and the tips of 

 the cells fuse. The cell resulting from this fusion begins 

 to grow, branching more or less, and becomes surrounded 

 in most cases by a mass of hyphae, which develop from 

 adjacent hyphal threads. The branches of the fertilized 



