V.] MOULDS. 33 



the substance of the horse-dung, and are the hyphce. Each 

 hypha is, as in Pemcillium, a tube provided with a tough 

 thickish structureless wall, which is partly composed of cel- 

 lulose, and is filled by a vacuolated protoplasm. In old 

 specimens, transverse partitions, continuous with the walls of 

 the hyphae, may divide them into chambers or cells. 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 intermediate substance. When the spo- 

 rangium 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 

 adheres 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 the same 

 composition as the wall of the hypha, which incloses a 

 mass of protoplasm. 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 prolonga- 

 tions. 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 hypha3 proceed from the spore as a centre, 

 their development gives rise, as in Penicillium, to a delicate 

 M. 3 



