ACTION OF ALPHA-CROTONIC ACID ON PLANTS 
179 
In regard to the exact mechanism of the chemical or physiological 
character of the interactions between crotonic acid and the nutrient salts, 
nothing definite can be said. The work thus far shows unquestionably 
that phosphate^ have an effect on the behavior of the crotonic acid towards 
plants; the data as a whole point to the conclusion that the antitoxic action 
of phosphate salts on crotonic acid is due mainly to the phosphate radical, 
either without or within the plant. It is also Evident that the crotonic 
acid is less harmful in solutions of an alkaline character. The four experi- 
ments in which the crotonic acid was used in concentration of 25 parts 
per million were not all conducted at the same time. Each set of solutions 
containing crotonic acid is comparable only with the normal set which was 
run simultaneously. In the set of solutions in which calcium acid phosphate 
was used, the 66 cultures containing the crotonic ac^'d produced 35 percent 
less growth than the 66 corresponding cultures without the organic acid. 
A reduction of 28 percent in growth is noted between the 66 normal and the 
crotonic acid cultures where the mono-sodium phosphate was used, 18 percent 
between the two sets of 66 cultures where the neutral di-sodium phosphate 
was used, and a reduction of only 7 percent in the two sets of 66 cultures 
where the alkaline tri-sodium phosphate was used. In each case, however, 
the crotonic acid was more harmful in the solutions where the phosphate was 
absent or low; the toxicity decreased as the phosphate content increased. 
This was the case whether the phosphate was in the form of the calcium or 
sodium salt, or whether it was an acid, neutral, or alkaline salt. 
The metabolism of the plant as affected by the crotonic acid was studied 
by analyzing the solutions so as to determine the amount of P2O5, NO3, 
and K2O absorbed. In each of the experiments the plants in the crotonic 
acid solutions absorbed less P2O5, NO3 and K2O than did those in the corre- 
sponding culture containing no crotonic acid. The decreased absorption 
of each constituent was approximately the same. There seemed to be no 
interference with the absorption of any particular constituent more than 
with that of another. 
In the earlier work with cumarin, salicylic aldehyde, vanillin, and qui- 
none, the absorption of phosphate from solutions containing cumarin or 
salicylic aldehyde was more normal than that of nitrates or potash; the 
absorption of nitrates from cultures containing vanillin or dihydroxystearic 
acid was more normal than was the absorption of phosphates or potassium ; 
and the absorption of potassium from cultures containing quinone was 
more normal than was the absorption of nitrates or phosphates. It is 
apparent that such compounds show markedly different physiological prop- 
erties and are very differently influenced by inorganic salts. Whether this 
physiological antagonistic action of phosphates towards crotonic acid is a 
direct action of the salt on the organic compound or whether it acts through 
the medium of the plant cell cannot be definitely stated.. 
