52 VEGETATION OF YEAST. 



additional cells. By the time that five or six vesicles are found 

 in each group, the fermentation is sufficiently far advanced for 

 the purposes of the brewer ; and he then takes measures to check 

 it, by which the vegetation of the yeast is suspended. The groups 

 of vesicles then separate into individuals, resembling those which 

 first constituted the yeast ; and thus a greatly-increased amount 

 of this substance is the result of the process. 



57. The process of fermentation consists, as regards the fluid, 

 in the conversion of the solution of sugar, into alcohol or spirit of 

 wine ; and this is effected by the action of the vegetating fungus, 

 which withdraws from the fluid, for the supply of its own 

 growth, that portion of its elements which constitutes the dif- 

 ference between sugar and alcohol. A process very similar to 

 this takes place when the common Mould, growing upon the 

 surface of a sweet preserve, causes its fermentation. The little 

 plant bears considerable resemblance to the Red Snow ; but 

 differs from it in the two following important particulars. The 

 Red Snow can flourish, when supplied with air and moisture 

 alone, the conditions which have been mentioned as favourable 

 to the growth of the Algse ; whilst this Yeast-plant can only 

 grow in the solution of vegetable matter, which is ready to 

 undergo decomposition, and which yields it a kind of nutriment 

 that the Red Snow does not require, but which is necessary for 

 the growth of all the Fungi. This is an instance, then, of what 

 was formerly stated, respecting the close resemblance between the 

 lowest forms of these simple tribes, which differ from one another 

 more in the conditions necessary for their respective growth, 

 than in their own structure. The other point of difference con- 

 sists in the extension of the Yeast-plant by buds, that is, by the 

 formation of new cells as continuations from the old ones, as well 

 as by the formation of separate germs ; whilst the Red Snow is 

 propagated by the latter only. It is interesting to trace, in a 

 being so extremely low in the scale, the two kinds of Reproduc- 

 tion, which are performed in a manner so much more complex, 

 and apparently so different, in the higher plants. 



58. The growth and reproduction of the more complex kinds 

 of Fungi, differs in no essential particulars, from the correspond- 



