442 THE GERM-PLASM 



plasma ') . The latter is derived directly from the former, from 

 which the plant in question — or one of its ancestors, if the 

 plant itself was raised from a cutting — arose. If, during the 

 growth of a tree, one of the determinants, N, varied in the same 

 way in certain ids. and tended, for example, to produce red 

 leaves instead of green ones, red leaves would nevertheless not 

 be produced till all, or at any rate a majority, of the determi- 

 nants N had become transformed into the red variety. If a 

 '■ reducing division ' intervened between the germ-plasm of the 

 bud and the growth of the latter into a shoot, a minority of ' red ' 

 determinants might give rise to a majority in one of the two 

 daughter-cells ; but this reducing division is exactly what does 

 not take place in ordinary cell-multiplication. 



Since bud-variations are of very rare occurrence, and only 

 one of many thousand buds on the sa?ne plant varies so as to 

 produce red leaves, for instance, while the altered conditions 

 simultaneously affect all the buds, I conclude that the modified 

 determinants which the tree contains 7nay so)neti))ies attain a 

 majority i?i consequence of an abnormal differential nuclear 

 division. Should this take place in the apical cell or cells 

 of a bud, the resulting shoot might, to return to our former 

 example, bear both green and red leaves ; for, according to our 

 pre-supposition, the 'green' and 'red' determinants of the 

 apical cells would have been separated during the cell-divisions 

 in such a manner that in some leaves the green determi- 

 nants, and in others the red ones, might be in the majority. 

 If the separation occurs at an earlier stage, before the apical 

 cells are formed, — that is to say, in the cambium, — a shoot 

 bearing red leaves alone might arise from the cell which 

 receives the ' red ' group at the ditTerential division of the 

 nucleus. 



There is nothing impossible about this assumption ; for during 

 the process of mitotic nuclear division, irregularities might occur 

 in the complex apparatus by which this process is effected, 

 and individual cases of such irregularity have actually been 

 observed : — even the possibility of a direct nuclear division 

 cannot be entirely overlooked. I am, however, far from con- 

 sidering this hypothesis as established, and merely offer it as a 

 suggestion. 



Nageli was of the opinion that all variations are slowly 

 prepared in the idioplasm in the course of generations before 



