314 
RICHARD M. HOLMAN 
the negatives upon co-ordinate paper. Marks made upon the roots 
by means of Chinese ink and which appeared in the photographs made 
it possible to so mount the prints upon the co-ordinate paper that the 
course of the curvatures could be easily studied and compared. No 
roots were used which were longer than 6 cm. and the roots under 
comparison in any series were of the same length. 
In the case of roots placed horizontally in air, loose sawdust and 
compressed sawdust, the first evidence of the beginning of the geotropic 
Fig. 7. Diagram showing the course of the primary curvature of main roots 
of Vicia faba placed horizontal in air and in compact moist sawdust. The heavy 
perpendicular lines cross the roots at points originally i cm. from the extremity. 
The broken lines indicate the original position of the extremity of the roots. For 
further comment see the text. 
curvature was a slight downward asymmetry of the root tip. This 
appeared at about the same time in the case of the roots in air and of 
those in loose sawdust and before the roots had undergone any appre- 
ciable elongation. Roots in compact sawdust, on the other hand, 
did not exhibit an asymmetry of the tip until they had undergone an 
appreciable elongation. (See S2 and A 2 in figure 7.) The first ap- 
