472 SYSTEMATIC BOTANY. 



tion than others in the possession of cilia by which motion is effected. 

 They usually multiply by simple segmentation; but in such cases 

 as Bacillus an apparent reproduction by means of sporules has been 

 observed. It is probable that some of these organisms are stages 



Fig. 518. Fig. 519. 



Fig. 518. Various species of Bacterium. 

 Fig. 519. Bacterium termo, magn. 2400. 



of some more perfect plant. The small Schizomycetes called 

 Bacteria are often found growing on the mucous surfaces of living 

 bodies and on wounds, &c. ; and on this subject there has arisen an 

 extensive literature, which is of more medical than botanical 

 interest ; and there is no doubt that, in a great multitude of cases, 

 the observers have mistaken the products of the decomposition of 

 organic bodies and crystalline precipitations of an inorganic nature 

 for Bacteria. Whether the Bacteria are the real causes of fermen- 

 tation and of various diseases, or whether they are merely 

 concomitants of those processes, is a debated point upon which 

 it is impossible to enter here. 



Allied to the Schizomycetes, though of a higher organization, 

 is the genus Saccliaromyces (or Torula}, to which the Yeast-plant 

 belongs. The Yeast-plant consists of single, roundish minute cells 

 of greater size than those occurring in the Schizomycetes. It 

 inhabits fluids which contain sugar, in which it excites alcoholic 

 fermentation. The cells contain true protoplasm, which can easily 

 be recognized as such, and in which vacuoles are usually to be found. 

 They multiply by simple exogenous or endogenous segmentation 

 (fig.'l A, p. 8, fig. 587, p. 552). 



The life-history of the Yeast-plant is further treated of under 

 the head of Nutrition in Cellular Plants, to which the student is 

 referred (see p. 552.) 



