GEMMATION AND GENERATION. 333 



the cells are attached, a filament is formed, and the 

 plant is said to grow ; when the cells are detached, a 

 new plant is said to be generated : but whatever dif- 

 ferences there may be between twenty cells forming 

 a filament, and twenty cells existing separately, each 

 capable of growing into a filament, the origin of both 

 is one and the same, and the process of Growth is 

 identical with the process of Generation. 



In a former passage I suggested that it was pro- 

 bably owing to difi'erences of temperature, or food, 

 that Eeproduction by Gemmation and by Generation 

 took place. This, which was hypothetical as regards 

 the Polyj^e, can be demonstrated in the Yeast plant. 

 There are two kinds of yeast, or rather two forms of 

 the same plant. The one is called surface yeast, the 

 other sediment yeast. The former requires a temper- 

 ature of 70° to 80° Fahrenheit ; the latter 32° to 45°. 

 Under the microscope we can watch the process of 

 Reproduction in each. The surface yeast grows by 

 budding only : from the cell-wall a little hernia is 

 formed, which grows and grows, until in lieu of one 

 cell there are two ; these two set up the same budding 

 process, and a whole filament of cells is the result. 

 The sediment yeast does not bud ; its isolated cells 

 burst, and liberate a quantity of nuclei (spores?) which 

 develop into perfect cells. If, however, the tempera- 

 ture be raised from 45° to 70°, this process is arrested ; 

 no more spores are formed, but the plant begins bud- 

 ding like surface yeast. Here, by a simple change in 

 one of the conditions only (that of temperature), we 



