V.] MOULDS. 37 



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 con- 

 verted into a sporangium, such as that already described, 

 whence spores are produced, w^hich give rise to the ordinary 

 stellate mycelium. Thus, Mticor presents what is termed an 

 "alternation of generations.'" The zygospore resulting from 

 a sexual process developes into a rudimentary mycelium, 

 with a single sporangium which constitutes the first gene- 

 ration (A], This gives rise, by the asexual development of 

 spores in its sporangium, to the second generation (B), 

 represented by as many separate Mncores as there are 

 spores. The second generation (B} may give rise sexually 

 to zygospores and so reproduce the generation (A); but, 

 more usually, an indefinite series of generations similar to 

 () are produced from one another asexually, before (A] 

 returns. 



When Mucor is allowed to grow freely at the surface of 

 a saccharine liquid, it takes on no other form than that 

 described; but, if it be submerged in the same liquid, the 

 mode of development of the younger hyphse becomes 

 changed. They break up, by a process of constriction, 

 into short lengths, which separate, acquire rounded forms, 

 and at the same time multiply by budding after the manner 

 of Torulis. Coincidentally with these changes, an active 

 fermentation is excited in the fluid, so that this " Mucor- 

 Torula" functionally as well as morphologically, deserves 

 the name of ' yeast.' 



If the Mucor-Torula is filtered off from the saccharine 

 solution, washed, and left to itself in moist air, the ToruLs 



