XIII.] MOULDS. 423 



now readily bursts, and the spores are separated by the 

 swelling and eventual dissolution of the gelatinous inter- 

 mediate matter. 



There appears to be no limit to the extent to which the 

 Mucor may be reproduced by this process of asexual de- 

 velopment of spores, by the fission of the contents of the 

 sporangium ; nor does any other mode of multiplication 

 become apparent, if the mould be grown in a fluid medium 

 and abundantly supplied with nourishment. 



But when growing in nature, a method of reproduction 

 is set up which represents the sexual process in its simplest 

 form, such as we have already seen in Spirogyra. Adjacent 

 hyphae, or parts of the same hypha, give off short branches, 

 which become dilated at their free ends, and approach one 

 another, until these ends are applied together. The proto- 

 plasm in each of the dilated ends becomes separated by a 

 septum from that of the rest of the branch ; the two cells 

 thus formed open into one another by their applied faces, 

 and their protoplasmic contents becoming mixed together, 

 form one spheroidal mass, to the shape of which the coa- 

 lesced cell-membranes adapt themselves. Here, as in Spi- 

 rogyra, the product of conjugation is termed a zygospore. 

 Its cellulose coat becomes separated into an outer layer 

 of a dark blackish hue and an inner colourless layer. 

 The outer coat is raised into irregular elevations, to 

 which corresponding elevations of the inner coat cor- 

 respond. 



Placed in suitable circumstances, the zygospore does not 

 immediately germinate ; but, after a longer or shorter period 

 of rest, the walls burst, and a bud-like process is thrown 

 out, which grows out into a mycelium. Under favourable 

 conditions this may at once assume the normal develop- 

 ment, but if the supply of food be scanty, the mycelium 



