GROWTH AND GENERATION. 313 



Let US now examine the old position, wliich declares that 

 the union of two different elements, a germ-cell and a 

 sperm-cell, is the act of Generation — an act sui generis, 

 and altogether distinct from the act of cell-multiplication, 

 or Growth, which is regarded simply " as a modification 

 of the nutritive function." The act of anion, hitherto re- 

 garded as the fundamental act of all Eeproduction, is only, 

 I believe, a subsidiary, derivative process, and not by any 

 means the " ultimate fact " at which our researches must 

 pause ; a conclusion to which Goethe pointed when he 

 showed that Growth and Eeproduction in plants are but 

 different aspects of the same law. 



Let us consider the known facts of Eeproduction in their 

 ascending order of complexity. What is the simplest pro- 

 cess known ? It is that of a cell spontaneously multiplying 

 itself by subdivision. In the albuminous and starchy fluid, 

 named protoplasma, a single cell appears. It assimilates 

 more and more of the fluid. It then divides into two cells 

 perfectly similar. These two cells divide into four, eight, 

 sixteen, and so the multiplication continues, till there is a 

 filament of cells, each independent and capable of separate 

 existence, but each attached to the other by its cell-wall. 

 In a similar way leaves, instead of filaments, are formed. 

 Many of the lower plants are nothing but aggregations of 

 such cells ; and in many this simple mode of Eeproduction 

 is the only mode yet discovered. By this process of sub- 

 division a single cell of the Protococciis nivalis (or red snow) 

 will redden vast tracts of snow in a few hours ; and tlie 



Bovista giganteum is estimated to produce in one hour no 



2 D 



