v.] MOULDS. 35 



apparent, so long as the mould grows in a fluid medium and 

 is abundantly supplied with nourishment. 



But when growing in nature, in such matters as horse- 

 dung, a method of reproduction is set up which represents the 

 sexual process in its simplest form. Adjacent hyphse, 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 protoplasm 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 coalesced cell-membranes adapt 

 themselves. This process of conjugation evidently represents 

 that of sexual impregnation among higher organisms, but as 

 there is no morphological difference between the modified 

 hyphje which enter into relation with one another, it is 

 impossible to say which represents the male, and which the 

 female, element. The product of conjugation is termed a 

 zygospore. Its cellulose coat becomes separated into an outer 

 layer of a dark blackish hue, the exosporium, and an inner 

 colourless layer, the endosporium. The outer coat is raised 

 into irregular elevations, to which corresponding elevations 

 of the inner coat correspond. 



Placed in favourable circumstances, the zygospore does 

 not immediately germinate ; but, after a longer or shorter 

 period of rest, the exosporium and the endosporium burst, 

 and a bud-like process is thrown out, which, usually, grows 

 only into a very short unbranched hypha. From this hypha 

 a vertical prolongation is developed, which becomes converted 

 into a sporangium, such as that already described, whence 

 spores are produced, which give rise to the ordinary stellate 

 mycelium. Thus, Mucor presents what is termed an " alter- 

 nation of generations". The zygospore resulting from a 



3—2 



