414 BOTANICAL GAZETTE [JUNE 
| experiments are at best unsatisfactory, or they would have defi- 
nitely determined the functions of the root tip without contro- 
versy decades ago. Mine were as consistent as they are likely 
to be, or as can be expected from a method which does great 
violence to the health of the plant, and in which any unsteadi- 
ness in the operation may entirely alter the result. When no 
traumatic bending occurred, the growth of horizontal decapitated 
plants was straight for more than twenty-four hours, and nearly 
always for more than forty-eight. In the end there was usually 
a downward curving in the basal part of the hypocotyl, but 
never farther up, where the curve, if any, was in the other direc- 
tion. The downward curve usually occurred before a new grow- 
ing point became evident, as is the case too when the response 
is by the root.?. In every respect the part of the hypocotyl which 
would execute a positively geotropic curvature is influenced by 
removal of the root tip, just as the responsive zone of the root 
would be in older plants. The interval during which a wound 
suspends the geotropic perceptivity in older hypocotyls is a very 
few hours at most, instead of about two days. 
Better evidence than decapitation can yield is obtained from 
a careful study of the distribution of growth in length along the 
young root and hypocotyl, and its relation to the location of the 
curve. For a basis of comparison this relation is first shown with 
older plants, in which the root alone curves. The plants had 
been germinated two days, and were marked off in 1™ zones 
and placed horizontal at 10:30 a.m., November 19. The result 
at 4:00 P.M. the same day is tabulated. The first column is 
the length of the roots at the beginning of the experiment. 
After twenty-nine and a half hours the average growth had 
been 20™" and the curve was go°, at about the same place. 
After five and a half hours, at the first measurement, the most 
growth had been in zones 3 and 4, but I could not measure it 
accurately enough to include it in the table. The experiment, 
like all in which the contrary is not stated, had been carried on 
in saturated air. 
7 Literature in CZAPEK: Ueber den Nachweis der geotropischen Sensibilitat 
der Wurzelspitze. Jahrb. f. wiss. Bot. 35 : 314-5. 1900. 

