Pe eee ee ee 
1900] MECHANISM OF ROOT CURVATURE 41 
rapidity with which the curve took place. Only the first 0.5°™ 
was taken, because within the time stated the curve is confined 
almost exclusively to that region of the root. By taking the 
average of the roots tested, it was found that there is a greater 
differenceSbetween the lengthening of the concave side and that 
of normal straight roots, under the same conditions, than 
between the lengthening of the convex side and that of normal 
roots. In other words, the relative shortening of the concave 
side is greater than the relative lengthening of the convex side. 
This is further evidence against the supposition that the concave 
side is merely compressed. It has previously been mentioned 
that numerous observers have found a shortening of the concave 
side in stems of both monocotyledonous and dicotyledonous 
plants. 
In the early stages of the curvature the zone of maximum 
curvature does not coincide with the zone of maximum growth. 
Indeed the curve may be completed before the two coincide. 
This fact had been frequently noticed in many experiments, and 
twelve roots were observed with this especially in mind. From 
four to seven hours after branding, ten of the twelve showed the 
curve almost wholly in the first 0.5°", while the maximum 
growth of these same roots was in the second 0.5 from tip. 
Of thirty-one straight roots carefully measured, the two meas- 
urements being four hours apart in most of them, four showed a 
greater growth in the 0.5°™ nearest the tip, twenty in the second 
0.5°™ from the tip, and seven grew the same in both half centi- 
meters. Within’ twenty four hours of the time of branding, 
however, if growth continues, the zone of maximum growth 
meets the zone of maximum curvature and finally passes it. I 
Suspect, but have not proved, that this is the time when many of 
the curved roots tend to straighten. These results agree with 
those of Wiesner (78, p. 233). 
RELATION OF CONCAVE CORTEX AND AXIAL CYLINDER. 
A few roots were bent forcibly with the hand for about ten 
minutes and after lying a few minutes free in water they were 
