a^' PIIVSIOLOGICAL MORPHOLOuY 



55 



constitution, or, if the chemical constitutions be similar, by 

 differences in resistance to growth. That organs which differ 

 in shape very often are chemically different is a well known 

 fact. The formation of urea in the liver and the synthesis of 

 hippuric acid by the kidneys are the consequences of chemical 



differences. 



In this way we are led through the mechanics of growth to 

 a conclusion which forms the nucleus of Sachs' theory of 



Fig. 25. 



organization, namely, "that differences in the form of organs 

 are accompanied by differences in their chemical constitution, 

 and that according to the principles of science we have to 

 derive the former from the latter." According to Sachs there 

 are as many " spezifische Bildungsstoffe " in a plant as there 

 are different organs.^ 



1 J. Sachs, staff tind Form der Pffanzenorgane, Gesammelte Abhandlungen, Vol. 

 II, 1893. 



