GEMMATION AND GENERATION. 315 



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

 Under the microscope we can watcli the process of Eepro- 

 duction in each. The surface yeast grows by budding only : 

 from the cell-wall a little hernia is formed, which o-rows 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 temperature be 

 raised from 45° to 70°, this process is arrested ; no more 

 .spores are formed, but the plant begins budding like surface 

 yeast. Here, by a simple change in one of the conditions 

 only, (that of temperature), we convert indisputable Gemma- 

 tion into indisputable Generation — unless we obstinately 

 refuse to consider any reproductive process as a true genera- 

 tive act that is not preceded by the union of sperm-cell and 

 germ-cell — a refusal which would lead to the denial of 

 Generation altogether in vast regions of the vegetable and 

 animal kingdom. 



Having established this point, let us ascend a step, and 

 we reach the second form of Reproduction, which is the 

 union of two siinilar cells. This is named by botanists the 

 act of "conjugation." In a simple filament, consisting of 

 cells produced by fission, any two cells may unite ; theii- 

 contents coalesce to form a new starting-point, from which 

 the multiplication of cells may proceed. Instead of two 

 cells in the same filament, two cells of contiguous filaments 

 may coalesce, but in each case it is the union of two similar 

 cells. This is the first dim indication we obtain uf that 



