1894. ''PREFORMATION OR NEIV formation:' 189 



from heirs-unequal division, it had also a stock of unaltered 



germ-plasm ready to be called into activity by unwonted stimuli. 



But even this hypothesis would not account for cells distorted 



by compression responding with the production of unwonted 



symmetries. 



V. — Vegetative Affinities. 



It will now be clear that Hertwig considers that all cells, in 

 addition to their apparent characters, possess, in addition, all the 

 characters of the species. 



For instance, histologically considered, the similar tissues in a 

 group of animals such as the mammalia, are, in most cases, not to be 

 distinguished. No doubt an expert could, in some cases, distinguish 

 through the microscope the red blood corpuscles of certain mam- 

 malian groups from each other ; but he could not do so in the case of 

 species, while with most tissues — connective tissues, nervous tissues, 

 muscular tissues — it would be only in rare and extreme cases that he 

 could distinguish one mammal from another. 



But, in addition to their visible structure, which bears an obvious 

 relation to their function, Hertwig attributes to each cell hidden con- 

 stitutional or specific characters. This is the case plainly enough 

 with the sexual cells. From indistinguishable ova and spermatozoa, 

 there arise animals with different specific, generic or even family 

 characters. But the facts of translation and transfusion for animals 

 and grafting for plants, show that there is a parallel between tissue- 

 cells and sex-cells so close as to suggest that tissue-cells are as much 

 specific as sex-cells. 



In plants, the operation of grafting is very easy to bring about ; 

 yet it is found that the approximated shoots will not always unite ; 

 if the cases where grafting succeeds and fails be considered, it is 

 found that they are parallel to success or failure in sexual crossing. 

 Near allies will unite, but failure follows the attempt to bring 

 together shoots from different species. There are, it is true, some 

 notable exceptions — cases where plants, considered closely allied, 

 will not unite, and cases where plants, regarded as specifically 

 separate, will unite. Grafting follows, not the apparent outward 

 tokens of resemblance, but the vegetative affinities of the cells. It 

 is their latent constitutional characters, and not their patent tissue 

 characters, that are at work. It is upon the experiments of Voechting 

 that most of these conclusions depend. He found in the case of 

 the pear and the apple, which belong to the same genus, that grafts 

 would not succeed, and in their case sexual crossing will not occur; 

 but the pear and the quince do graft, although these belong to 

 different genera. Hertwig thinks it probable that sexual affinity and 

 vegetative affinity depend upon the same ground characters of the cell. 



Voechting calls the grafting of twig and stem havmonic when a 

 full individuality is reached, disharmonic when this is not the case. 

 When the disharmony is complete the two either poison each other 



