§ 3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 483 



cally stimulating agent, we have recently gained valuable data 

 from the studies of CzApek ('98). He has found that the 

 stimulated protoplasm, for instance, of a geotropic radicle 

 exhibits no visible movements or negative electrical variation, 

 as in the nerve cells of animals, but does exhibit a chemical 

 change. Thus, when the root tip of the seedling of a bean or 

 other species is boiled in a solution of ammoniacal silver 

 nitrate, there is a marked reduction of the silver, especially in 

 the cells of the periblem. This reduction is stronger in the 

 cells of stimulated root tips than in those of unstimulated 

 ones. A second change consists in the diminution in the 

 amount of a substance of the root tip which easily loses oxy- 

 gen. Such a substance is indicated by such changes as these 

 in the normal root tip : blue coloration (oxidation) of a sec- 

 tion of the tip when placed in an emulsion of guaiac gum in 

 water ; deep blue coloration of sections by indigo white * ; 

 strong violet reaction (indophenal reaction) in sections sub- 

 jected to an aqueous solution of a-naphthol to which paraphe- 

 nylendiamin has been added. Now all such reactions are less 

 marked in the root after stimulation. We conclude that stim- 

 ulation results in increased capacity for reduction and dimin- 

 ished capacity for oxidation — an increase in the avidity for 

 oxygen. 



These changes occur long before the response of turning 

 shows itself ; they occur earlier in the non-sensitive roots, 

 and they are less marked after a slight stimulus, such as 

 results from a slight inclination of the root from the vertical 

 position. 



The isolation of the two substances, the reducing and the oxidizing, was 

 now attempted. The former is not changed by boiling or by the action of 

 chloroform, and is soluble in alcohol; the latter is destroyed by heat, is 

 unchanged by chloroform, is insoluble in alcohol, and may be extracted 

 from the triturated cells by water. A large number of root tips of Vioia 

 faba were rubbed up with water until no fragments remained. This aque- 

 ous extract was filtered, and to the filtrate alcohol was added. A precipi- 

 tate occurred, which had all the properties of the oxidizing substance. It 

 is highly probable that it belongs to the category of oxidation ferments. 



* This is made by the cautious reduction of indigo carmine by dilute hydro- 

 chloric acid and zinc. 



