No. 502] CHEMICAL MECHANICS IN LIVING PLANT 653 



of days to double its weight! Construction of the curves 

 of growth through the season will show whether it is this 

 or some other alteration in the form of the curve. 



I now propose to say a few words about one last point 

 in connection with growth considered as a phenomenon of 

 catalysis before passing on to deal with the effects of 

 temperature. 



Of the metallic elements that are essential for the 

 growth of plants some occur in such minute quantities 

 that one can only imagine their function is catalytic. If 

 iron, for instance, played any part in metabolism which 

 involved its being used up in any building material or 

 by-product of metabolism, then a larger amount than actu- 

 ally suffices should be advantageous. If its function is 

 catalytic the iron would go on acting indefinitely without 

 being consumed, and so a minute trace might serve to 

 carry out some essential, and even considerable, sub-sec- 

 tion of metabolism. 



Elements like manganese, magnesium and iron are 

 often associated with non-vital catalytic action, and a 

 preparation of iron has recently been quantitatively in- 

 vestigated which seems to have literally all the properties 

 of an organic oxydase from plant tissues. 11 



As long ago as 1869 Raulin observed that traces of un- 

 essential salts, in particular those of zinc, added to the 

 culture medium in which he grew the fungus Sterigmato- 

 cystis caused a rapid acceleration of the growth rate. 

 The time that the mycelium took to double its weight was 

 now reduced to a half or even a third. This continued 

 enormous effect of so small a trace of substance is pos- 

 sibly to be regarded as an added catalyst to the normal 

 protoplasmic apparatus. This sort of effect is currently 

 labeled "chemical stimulation" and has been interpreted 

 as an attempt of the fungus to grow away from an un- 

 pleasant environment. To me it looks as if such chem- 

 ical stimulation were really another example of the in- 



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