XIII.] MOULDS. 421 



and is filled by a vacuolated protoplasm. In old speci- 

 mens, transverse partitions, continuous with the walls of 

 the hyphae, may divide them into chambers or cells, but 

 the plant is as a rule unicellular, or rather non-cellular, 

 as regards its vegetative organs. The hyphce contain very 

 numerous nuclei. The stalk of the sporangium is a hypha 

 of the same structure as the others. The wall of the 

 sporangium is beset with minute asperities composed of 

 oxalate of lime, and it contains a great number of minute 

 oval bodies, the spores^ held together by a transparent in- 

 termediate substance. When the sporangium is ripe, the 

 slightest pressure causes its thin and brittle coat to give 

 way, and the spores are separated by the expansion of 

 the intermediate substance, which readily swells up and 

 finally dissolves, in water. The greater part of the wall 

 of the sporangium then disappears, but a little collar, 

 representing the remains of its basal part, frequently ad- 

 heres to the stalk. The cavity of the stalk does not com- 

 municate with that of the sporangium, but is separated 

 from it by a partition, which bulges into the cavity of 

 the sporangium, forming a central pillar or projection. 

 This is termed the columella and stands conspicuously 

 above the collar, when the sporangium has burst and the 

 spores are evacuated. 



The spores are oval and consist of a sac, having nearly 

 the same composition as the wall of the hypha, which 

 encloses a mass of protoplasm and a nucleus. When they 

 are sown in an appropriate medium, as for example in 

 Pasteur's solution, they enlarge, become spheroidal, and 

 then send out several thick prolongations. Each of these 

 elongates, by constant growth at its free end, and becomes 

 a hypha, from which branches are given off, which grow 

 and ramify in the same way. As all the ramifying hyphse 



