CHAP, iv.] REPRODUCTION OF PLANTS. 117 



belonging to two distinct cells, respectively male and 

 female, which form a single cell. The above examples 

 illustrate the primitive form of asexual reproduction, 

 which involves the destruction or loss of individuality of 

 the parent plant, but commencing with the Algas and 

 running through most groups of Cryptogams we find a 

 higher asexual mode, where specialized and usually com- 

 paratively small portions of the individual are told off 

 for the purpose ; such portions fall away when mature, 

 and in many cases are not distinguished popularly from 

 sexually produced seeds. Although the sexual method 

 of reproduction is universal in phanerogams, yet the 

 primitive asexual method has not completely died out, 

 but manifests itself in a variety of ways. As examples, 

 the propagation of plants by cuttings, which may be 

 considered analogous to the breaking up of a Nostoc 

 into portions capable of reproducing the species or kind, 

 thus proving that all the essentials constituting the life 

 of the individual are present in the protoplasm of every 

 cell ; whereas in the great number of plants that cannot 

 be reproduced vegetatively by cuttings or other asexual 

 methods, the protoplasm has become more sharply diffe- 

 rentiated into series, one capable of governing the work 

 necessary for the existence of the individual, the vege- 

 tative portion, and incapable of exercising the functions 

 necessary for reproduction ; a second concerned specially 

 with reproduction, but with little capacity for vege- 

 tative work. The tubers of the potato and bulbs are 

 also asexual modes of reproduction still retained by 

 phanerogams. 



Sexually formed reproductive bodies, known as seeds 

 in the higher plants, originate, as already stated, from a 



