WEISM 'ANN'S THEORY OF THE GERMPLASM 77 



of the vegetative affinities between tissues exactly 

 as one speaks of the sexual affinities between repro- 

 ductive cells. 



SUMMARY OF THE CONCLUSIONS IN THE FIRST 



SECTION. 



Summing up what has been said in the pre- 

 ceding pages, we find a large series of facts sup- 

 porting our contention that cells multiply only by 

 doubling division. First comes the fundamental 

 circumstance that single-celled organisms exhibit 

 only doubling division, as by that alone the per- 

 manence of species, which experience shows us to 

 exist, is possible. 



Secondly, some facts of reproduction were con- 

 sidered. The formation of germinal tissues, and, 

 in the case of lower plants and animals, the occur- 

 rence of budding in almost any part of the bod} 7 , 

 are easily intelligible if every cell, like the egg- cell, 

 has been formed by doubling division, and so 

 contains the rudiments of all parts of the organism; 

 and if thus, on the call of special conditions, every 

 cell may become a germ-cell again. 



Thirdly, great stress is to be laid on those ex- 

 periments in which the process of development was 

 interfered with at different stages, as these showed 

 that the separate cells which arose by division were 

 not predestined unalterably for a particular role, 

 according to a predetermined plan (facts of re- 

 generation and heteromorphosis). 



Fourthly, the results of grafting, transplantation, 

 and transfusion indicate that the cells and tissues 



