OUR COMMON MOULDS. 



401 



quires a diameter much greater than that of the filaments which have 

 produced it, and is many hundred times the size of the spores formed 

 in the capsules. It is also provided with two coats, the outer one 

 thick, dark-colored, and covered with warty excrescences, except on 

 the two ends where the remnants of the conjugated filaments remain. 

 Successive stages in the development of these spores are shown in 

 Fig. 3. At a the two swollen threads are near each other ; b, the pro- 

 cess partly completed, with the middle cell plainly seen ; and c, the full- 

 formed zygaspore, with the remains of the old cells. The importance 

 of these sexual spores in the economy of the plant is not difficult to 



Fig. 3. Zygospores of Mccor Stztgites. Do Bary. 



understand. The minute asexual spores have a very thin covering, 

 and under favorable conditions will germinate as soon as formed, but 

 on the other hand are readily destroyed by extreme climatic changes. 

 The large, well -protected zygospores which germinate only after 

 months of ripening, are in every way fitted to carry the species 

 through the unpropitious season of winter, times of drought, and 

 severe exposure. When the zygaspore germinates it produces very 

 soon a large crop of capsules, and their little spores are scattered 

 far and wide ready to develop into plants in a few hours, as circum- 

 stances shall decide. This dual form of fruiting is an interesting 

 feature in the life of these little plants, and is as effectual in preserv- 

 ing the species as it is interesting. 



After upward of a week from the time the Miicor, of which we 

 have been speaking, made its appearance on the bread, another mould 

 was noticed growing- over its surface, which was of a rnuoh finer struct- 

 ure and dingy yellow in color. When placed under the microscope, 

 it was found to be peculiar, both in structure and habit of growth. 

 The filament which bears the spores, as it rises from the matted sur- 

 face of the Mucor, divides into two branches, each of these into two 

 others, and so on, until ten or more branches are reached. The same 

 angle of divergence being preserved in all the branching, the com- 



TOL. IX. 'i 



