1915] HARVEY— ETHYLENE 21 1 



concentrations which are in reality; for example in the case of 

 chloroform or ether, thousands of times stronger. Probably most 

 of the ether concentrations employed by Hempel (ii) were many 

 times weaker, physiologically, than the ethylene concentrations of 

 the above-described experiments. Such an assumption would 

 account for the difference between some of her results and those 

 reported in this paper. It seems probable that ethylene, also, 

 would favor condensation processes if used in " weak " or "medium" 

 concentrations. 



In the presence of ethylene the simple soluble substances in- 

 crease at the expense of the higher soluble and insoluble forms; 

 direct reducing sugars against soluble non-reducing sugars and 

 insoluble polysaccharides; amino acids and amids against proteins; 

 and probably fatty acids and glycerine against fats, seeing that the 

 latter were found to diminish. Accordingly, ethylene appears to 

 affect the balance of the general chemical reactions of the plant 

 in favor of the simpler substances. The experimental work offers 

 no evidence as to whether or not this result is accomplished through 

 an acceleration of the hydrolytic as well as through a retardation 

 of the condensation processes, since all the substances present in 

 the tissue examined (epicotyls) had, within a relatively few hours, 

 arrived, in simple translocation forms, from the cotyledons. 



The accumulation of soluble substances in the tissue changes 

 the osmotic relations of the cells and may have much to do with 

 the observed swelling of plant organs in the presence of ethylene, 

 for example in the characteristic "horizontal nutation" or "triple 

 response" of the pea epicotyl. Also, the observed retardation of 

 the rate of elongation may partly be accounted for by the fact that 

 the gas interferes with the synthesis of complex substances, that 

 is to say, perhaps with tissue formation. 



Summary 



1. Ethylene was found to be very effective in producing changes 

 in the general processes of plant metabolism. 



2. Chemical analyses showed that ethylene caused the simple 

 soluble substances to increase at the expense of the higher soluble 

 and insoluble forms. 



