54 



PLANT STRDCTUKES 



While the ordinary method of reproduction through the 

 growing season is by means of these rapidly germinating 

 spores, in certain conditions a sexual process is observed, 

 by which a heavy-walled sexual spore is formed as a resting 

 spore, able to outlive unfavorable conditions. Branches 

 arise from the hyphse of the mycelium just as in the forma- 



Fia. 36. Mature sporangium of ^fncor, ehowing 

 the wall {A), the numerous sjiores {C), and 

 the columella (5)— that is, the partition wall 

 pushed up into the cavity of the sporangium. 

 — Caldwell. 



Fic. 37. Bui'Sted sporangium of 

 Mucor, the ruptured wall not 

 being shown, and the loose 

 spores adhering to the colu- 

 mella.— I' aldwell. 



tion of sporophores (Fig. 38). Two contiguous branches 

 come in contact by their tips (Fig. 38, A), the tips are cut 

 off from the main coenocytic body by partition walls (fig. 

 38, B), the walls in contact disorganize, the contents of 

 the two tip cells fuse, and a heavy-wtilled sexual spore is 

 the result (Fig. 38, ('). It is evident that the process is 

 conjugation, suggesting the Conjugate forms among the 



