REPRODUCTION AND GROWTH 179 



conjugation or fertilization. The whole conditions of reproduc- 

 tion, in this mode, may, however, be greatly complicated by an 

 alternation of asexual and sexual reproduction. 



65^. Vegetative Reproduction. Simpler conditions than 

 the above ones are characteristic of many of the higher plants. 

 Such organisms may reproduce by '' buds," " grafts," " cuttings," 

 " slips," etc. Here the cells of the ordinary, somatic tissues can 

 divide, differentiate and undergo tectonic assembly so that another 

 plant which is of the same category as the parental one is repro- 

 duced from a small piece of the latter. The somatic cells, in such 

 a case are not strictly differentiated from germ-cells and most 

 cells in the fully developed organism must be regarded as repro- 

 ductive ones. 



Roses reproduce exclusively in this way (by apogamy). The 

 plants do not bear seed. Willows, poplars, sugar-canes, some 

 bananas, etc., reproduce by strictly asexual methods, and vegetat- 

 ively. 



65^. Budding in Animals. Similarly, some animals, the 

 familiar Hydra, for instance, may simply bud. A protuberance 

 forms on the outer parts of the body and this contains cells that 

 have formed by the divisions of some cells from each germ-layer 

 (see Section 70). The mass of cells forming the bud differentiate 

 and are assembled into a new organism of the category of that 

 one which formed the bud. Such cells are not germ-cells but 

 are simply somatic cells. The potencies for development of these 

 cells are, however, greater than are those which divided in the 

 parental body so as to form them. 



Again, there are innumerable modifications of the process of 

 budding in animals. The essential thing, however, is that small 

 " samples " of somatic cells can reproduce the whole body by 

 their reproductions. In such cells, as they are placed in the 

 parental body, there are qualities, or potencies, over and above 

 those of ordinary bodily functioning. 



66. ON SEXUAL REPRODUCTION 



The essential condition of sex is that the germ-cells are of 



two kinds, '' male " and " female." The male germ-cell, or 



gamete, is usually small and actively motile and it is called 



the spermatozoon in animal organisms. It is formed by the 



