46 THE GERM-PLASM 



the nuclear matter. In his opinion ' molecular stimuli are trans- 

 mitted from the nucleus to the surrounding cytoplasm, and, on 

 the one hand, control the processes of metabolism in the cell, 

 and on the other, give a definite specific character to the growth 

 of the cytoplasm, this growth being caused by nutrition.' Al- 

 though transmission of the molecular stimuli, proceeding from 

 the nucleus to the rest of the cell, is certainly conceivable, 

 de Vries has rightly shown that this is not a sufficient expla- 

 nation of the phenomena, because it takes for granted the fun- 

 damental point of the matter requiring explanation. If the cell 

 of any plant is to acquire the hereditary property of forming 

 malic acid, those pangenes in the cell-body which can produce 

 this acid could, it is true, come into play by molecular stimuli 

 being transmitted to them from the nucleus ; but this hypoth- 

 esis takes their presence for granted, and the main question as 

 to how these producers of malic acid get into the cell remains 

 unanswered. 



Haberlandt * has attempted to trace the control of the cell by 

 the nucleus to the enzymatic action of the latter, i.e., to the giv- 

 ing off from the nucleus of certain chemical compounds which 

 cause the cell-substance to become changed in a given manner ; 

 but this explanation is regarded by de Vries as insufficient, be- 

 cause here again it is necessary to presuppose a definite differen- 

 tiation of the cell-body. 



De Vries himself gives a solution of the problem, and his 

 hypothesis has, at any rate, the advantage of great simplicity 

 and lucidity. He supposes that some of the pangenes which 

 constitute the nuclear matter pass into the body of the cell 

 through the nuclear membrane, and there form its parts and 

 structures, of the qualities of which they are the special 

 bearers. 



Although I formerly inclined towards Strasburger's view, it 

 always appeared to me rather as a formal than as a real expla- 

 nation of the problem, and I regarded it more as a provisional 

 formulation than as a solution of the difficulty. In my opinion 

 de Vries's idea of the migration of minute, specific, vital parti- 

 cles from the nucleus into the cell-body affords an extremely 

 happy solution of the apparently inexplicable manner in which 



* G. Haberlandt, * Uber die Beziehungen zwischen Funktionen und Lage 

 des Zellkerns,' 1877. 



