172 
Journal of Agricultural Research 
Vol. VIII, No. 5 
application of minute doses of other copper salts free from ammonia. 
Also in a first series of experiments using 2 per cent ammonia water 
(0.837 P er cent °f actual ammonia) and 5 per cent ammonium carbonate 
he obtained warts, but, as these solutions had been applied by means of 
an atomizer which had previously contained the copper solutions, the 
oligodynamic effects of copper were suspected and the experiments with 
the ammonia and ammonium carbonate were repeated, using brushes so 
as to exclude copper contamination, but then with more or less con¬ 
tradictory results, so that the author was in doubt as to the action of 
ammonia, and concludes the paragraph as follows: 
While several of the sprayed spots undoubtedly formed intumescences as a result 
of spraying with ammonium carbonate or ammonia, owing to the negative results of 
several plants it will not be possible without further tests to definitely ascribe the 
formation of these intumescences to the ammonia. 
For this reason also, no doubt, he does not mention ammonia as a 
cause of intumescences in his general summary, which I quote: 
The results of the present investigation may be briefly stated as follows: 
1. Cauliflower plants sprayed with copper ammonium carbonate produced large 
numbers of intumescences as a direct result of the spraying. 
2. Similar intumescences were produced by means of weak solutions of copper 
chloride, copper acetate, copper nitrate, and copper sulphate when sprayed in very 
fine drops on the surface of the leaves. 
3. The intumescences were formed in larger numbers on the lower surface of the 
leaves than on the upper surface of the leaves. 
4. Intumescences were formed independent of soil or atmospheric conditions, so 
that the heat and water supply had nothing to do with their formation. 1 
5. Intumescences must be regarded as the result of the stimulating activity of 
chemical poisons, sprayed upon the leaf in weak solutions. 
6. The stimulating activity exerted is probably due to the formation of compounds 
within the cells of high osmotic tensions, these compounds being either compounds 
formed by the copper salts with parts of the protoplast, or compounds formed as a 
result of a stimulus exerted, as evidenced by the presence of large amounts of oxidiz¬ 
ing enzymes 2 [2 per cent gum guaiac test] as a result of an indirect stimulus exerted 
by the salts sprayed upon the leaf surface. 
Rosen (14), who repeated Von Schrenk’s copper-ammonium-carbonate 
experiments on cauliflower and extended them to cabbage with positive 
results on both plants, speaks only of the copper stimulus and apparently 
did not suspect the ammonia, but to me the presence of that very dif¬ 
fusible compound in suitable dilution explains in conjunction perhaps 
with carbon dioxid by far the larger part of the observed action. 
To test out my conclusions respecting ammonia as the probable tumor 
stimulus, I first injected, in a preliminary way, small quantities of strong 
ammonia water (aqua ammonia, sp. gr. 0.90,1 part, and distilled water 10 
parts) into the young internodes of large castor-oil plants (Ricinus com- 
1 Excessive water supply and excessive heat are believed to cause intumescences on gr* *ape leaves. See 
Von Schrenk’s papers (7, 8). 
* Crowngalls also are very rich in oxidizing enzyms (1, p. 173)- 
