

CHAPTER I. 



YEAST REPRODUCTION NUTRITION FERMENTATION 

 SPIROGYRA NUTRITION TRADESCANTIA-HAIR CELL 

 OF ELODEA-LEAF CELL OF THE PITH OF ELDER. 



YEAST is familiar as the cause of the process known as 

 fermentation, by which alcohol is produced from sugar. 



It is obtained from the brewers for use in the labora- 

 tory as a muddy brown fluid. The muddiness depends on 

 the same general cause that gives turbidity to dirty water, 

 namely the presence of innumerable very minute particles 

 suspended in the fluid. In the case of yeast each of these 

 particles is a simply organised plant belonging to the 

 great tribe of Fungi, and known as Saccharomyces 

 cerevisice. 



The plant is of the simplest possible structure, since it 

 consists of a single cell : it has nevertheless the attributes 

 of a more highly organised plant, it leads an individual 

 existence and is able to feed, to grow, and to reproduce 

 itself. 



The yeast cell, like those which build up the tissues of 

 more complex plant-bodies, consists of a mass of proto- 

 plasm surrounded by a cell-wall. It is possible to make 



D. E. B. 1 



