308 AMERICAN JOURNAL OF BOTANY [Vol. 9. 
RATE 
180 r 
0 90 80 
MIN 
Fig. I. Curves showing the rate of respiration of wheat seedHngs (expressed as per- 
centage of the normal rate), in lactic acid 0.0025M, o.oiM, 0.04M, ando.iikf. The normal 
rate (which is taken as 100 percent) is the reciprocal of the time required to change the indi- 
cator from pH 7.36 to pH 7.09 (usually from 30 to 60 seconds, according to the age of the 
material). The curve with 0.0025^/ lactic acid represents the mean of three experiments; 
probable error of the mean, less than 5 percent of the mean (after the maximum, less than 
2 percent of the mean). The curve with o.oiM acid is the mean of two experiments; 
probable error of the mean, less than 3 percent of the mean. The curve with o.04lf acid 
represents a single typical experiment. The curve with o.iM is the mean of five experi- 
ments; probable error of the mean, less than 10 percent of the mean. 
