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THE AMERICAN NATURALIST [Vol. XL V 



in greater or less degree seems to be the only plausible 

 one to-day — we are forced, in explaining morphogenesis 

 to postulate the existence of some time-, quantity- and 

 quality-controlling mechanism. The one evident class of 

 substances in the germ-cells which can fulfil the neces- 

 sities of the case are the ferments. For since they will 

 determine the velocities of chemical reactions they must 

 in consequence control the quantitative relations of the 

 cell chemistry at any given unit of time. But from the 

 very fact that where a large number of associated re- 

 actions are going on simultaneously, these quantitative 

 relations at given stages of the chemical interchanges 

 must profoundly influence qualitative results, we can not 

 but conclude that this initial control of velocities must 

 condition the qualitative results. 



If we regard the chromosomes as centers of such a 

 series of velocity-controllers, or, in other words, as 

 sources of various enzymes, we can at once appreciate 

 the necessity for having them so accurately balanced off 

 in size and particularly in their quantitative relations 

 one to another. For since the velocity of the reaction in 

 a fermentable substance is determined not only by the 

 presence of the ferment, but also by the amount of it, 

 the quantitative relations of the ferments to one another 

 would have to be very accurately maintained. 



What appears to be in a way a non-chromosomal 

 demonstration of this fact is found in connection with 

 the chloroplasts of plant cells which seem to exercise 

 their functions at least in part through the agency of 

 ferments. As is well known, in cell division these bodies 

 are each carefully divided and handed on to the daughter 

 .•ells so that a eonstancv in number and in general re- 

 lationships is maintained. 



But, it may be objected, what is to be done with those 

 cases of nuclear division in which the mitotic divisions 

 of the germ-cells have been preceded by a series of ami- 

 totic divisions? Wieman 10 has shown that in amitosis the 

 appearance of the division figures is by no means the 



