310 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
that in the case of wheat seedlings lactic acid is not an important stage in 
the normal metabolism. This is interesting in view of its apparent im- 
portance in the animal metabolism, and further experiments on animal 
tissues by this method should prove valuable. 
RATE 
Ol 1 1 1 : U 
0 75 150 225 300 
MIN. 
Fig. 2. Curves showing recovery from exposure to lactic acid. Normal rate as in 
figure I. Solid line represents respiration in lactic acid; broken line, respiration in dis- 
tilled water. Curve A in 0.2M acid, curves B and C in o.iM acid. Each represents a 
single typical experiment. 
Conclusions 
1. In high dilutions, such as 0.0025 Tkf, lactic acid first accelerates and 
then depresses the rate of production of carbon dioxide by wheat seedlings. 
2. As the concentration of the acid increases, the preliminary rise in 
rate becomes less marked, till a concentration is reached when the rate 
begins to fall at once. 
3. Even if the rate has been rapidly reduced to 25 percent of the normal 
by 2 ikf lactic acid, recovery is possible and appears to be complete. 
4. The observed effects are due not merely to osmotic pressure or to 
acidity, but to some specific action of the lactic acid. 
Since there is no permanent increase in the rate of production of carbon 
dioxide, as would be expected on the hypothesis that lactic acid is a stage 
in the metabolism of wheat, it may be concluded that lactic acid is not, in 
this case, an important intermediate substance. 
Laboratory of Plant Physiology, 
Harvard University 
