i68 
J. J. SKINNER AND F. R. REID 
trations of lo parts per million growth of tops was reduced lo percent, but 
the roots were not affected; in 25 parts per million growth was materially 
reduced, green weight of tops was reduced 27 percent, while the gro\vth of 
roots was checked; in concentrations of 100 parts per million growth was 
reduced 33 percent. The roots of the plants in this concentration made only 
Fig. I. Effect of a-crotonic acid on cowpeas and wheat. 
(i) Distilled water, (2) a-crotonic acid 10 parts per million, (3) 25 parts per million, 
(4) 50 parts per million, (5) 100 parts per million, (6) 200 parts per million, (7) 500 parts 
per million. 
a small growth; they were short and stunted. The harmfulness was still 
very marked in these high concentrations when calcium carbonate was added 
to the solutions. In weaker concentrations the effects were not so severe 
in[^the presence of lime. 
In figure i is shown the effect of various concentrations of the crotonic 
acid on wheat and cowpea plants grown in distilled water. The striking 
effect of the organic acid is here apparent. 
Nutrient Culture Solutions 
An extensive study was made, growing wheat plants in nutrient solutions 
of calcium acid phosphate, sodium nitrate, and potassium sulphate, without 
