1900] MECHANISM OF ROOT CURVATURE 45 
MEASURING CELLS. 
In measuring cells in Vicia faba roots it was found that in 
those which were strongly curved, most of the cells of the cor- 
tex on the concave side between the zone of the greatest curva- 
ture and the tip had their radial diameter longer than the 
diameter parallel to the long axis of the root. This is true to 
about 3™" from the tip of strongly curved roots, but beyond that 
point the cells elongate rapidly, so that the radial diameter 
becomes shorter than the one parallel to the long axis of the 
root. The fact that the cells in the region mentioned have the 
radial diameter greater than the other is positive proof against 
Kohl’s contraction theory as applied to these roots. Any contrac- 
tion necessarily takes place partially in this region, and according 
to Kohl’s theory the increased turgor shortens the longer diameter 
of the cells on a concave side. It is inconceivable, however, 
that the longer diameter could become the shorter one through 
increased turgor. Since the cell diameter parallel to the direc- 
tion in which the cells are supposed to shorten is less than the 
diameter transverse to that direction after the curve is produced, 
it is obviously impossible for the shortening of the concave side 
to be brought about as Kohl supposed. In the discussion of 
grass nodes Kohl himself writes (33, p. 49): “The transverse 
diameter of the concave cells is greater than the longitudinal 
diameter.” But Kohl evidently did not see that this condition 
invalidated his theory of curvature. 
WATER CONTENT OF CONVEX AND CONCAVE SIDE OF CURVING ROOTS. 
In a series of experiments I have determined that there is a 
greater relative amount of water in the convex half of curving 
roots than in the concave half, but this is just what should be 
expected if we take into consideration the enormously large 
vacuoles on the convex side as compared with those on the con- 
cave side. As I do not consider these results of very great 
importance, I shall not give them in full, but only a summary. 
The method was as follows: roots were branded as usual, 
and after the curve had made considerable progress, the roots 
