FERTILIZATION. 65 



priated from the inorganic world during the predominance 

 of life, to that condition on the cessation of life in a given 

 individual. It is not difficult to realize that this primitive 

 mode of reproduction, by division into two equal parts, of 

 an organism at the end of its vegetative phase, each portion 

 growing to the size of its parent and then repeating the 

 same process, could not possibly have become general, not 

 even from the point of view of supply and demand ; as by 

 this method of reproduction there was a continual drawing 

 from the available supply of plant food without any return, 

 except the small amount of certain elements furnished by 

 respiration. The change from this condition, and the 

 gradual evolution and differentiation of the sexual method 

 of reproduction, has however obviated the possibility of a 

 plant famine, due to all the readily available material having 

 been used up without a corresponding replacement. In the 

 sexual method of reproduction, the leading idea is the 

 mingling together of two distinct portions of protoplasm, 

 which together form a cell. From this one cell, which 

 constitutes the starting-point of a new individual, all tissues 

 of whatever nature entering into its composition are derived. 

 The two minute portions of protoplasm combining to form 

 such a sexually-produced cell may be derived from different 

 portions of the same plant, when the term self-fertilized is 

 applied ; on the other hand, cross-fertilization is brought 

 about by the two portions of protoplasm being derived from 

 different individuals of the same species or kind. 



Sexual reproduction, as already mentioned, is shadowed 

 in under the form of conjugation, where two apparently 

 similar portions of protoplasm, either under the form of 

 motile zoospores, or contained in cells as in Spirogyra, blend 

 together to form a sexually-formed reproductive body or 



