1 6 Outline of Genetics 



starts a line of purely body plasm cells. A similar 

 differentiation occurs between the granddaughter-cells 

 from the fully equipped daughter, and so on for two more 

 divisions, so that finally there are fifteen body plasm 

 cells and but one germ plasm cell; the germ cells of 

 the adult individual can all be traced to this single 

 initial. 



A somewhat similar program has been traced in Chry- 

 somelid beetles, where, after numerous segmentation 

 divisions, some of the nuclei associate with certain gran- 

 ules, and it is these nuclei that start the germ plasm. 

 Hegner (Doncaster 7) has succeeded in artificially 

 destroying these granules by means of a hot needle, 

 thus producing embr}'os without germ cells. 



Equally striking situations have been demonstrated 

 in other animals as well, but nothing of the sort has 

 ever been found in plants. Germ cells in plants are 

 formed from h^-podermal and even epidermal cells, 

 which, during earlier ontogeny, are apparently identical 

 with other somatic tissues. Here there is surely no dis- 

 tinct germ plasm, isolated from body plasm and insulated 

 within it from environmental influences. In fact, there 

 are cases in which ''adventitious" germ cells have been 

 seen to form from tissues which normally are quite as 

 somatic as any plant tissue could be. In this connection, 

 it is worth mentioning that Bateson (2) suspects plants, 

 as genetic machines, differ fundamentally from animals; 

 this idea being suggested to him in good part by the 

 fact that ''in the animal the rudiments of gametes are 

 often visibly separated at an early embryonic stage, 

 whereas in the plant they are given off from persistent 

 growing points." 



