ORIENTATION OF PRIMARY TERRESTRIAL ROOTS 303 
film of water, show no tendency to the acute and complete secondary 
curvature characteristic of roots in compact non-fluid media. 
Table VI 
Roots of Vicia faba var. equina Performing Geotropic Curvatures in Soils Containing 
Different Percentages of Water 
Original Position Horizontal 
Original Position Obliquely Upward (150°) 
Percentage of 
^^^^"^ Soif 
Root 
Number 
After 
I Cm. 
Growth 
After 
2 Cm. 
Growth 
Radius 
of Curva- 
ture 
Root 
Number 
After 
I Cm. 
Growth 
After 
2 Cm. 
Growth 
Radius 
of Curva- 
ture 
20% 
I 
2 
3 
4 
64° 
37° 
14° 
65° 
29° 
17° 
14° 
10 mm. 
10 " 
11 " 
20 " 
I 
2 
82° 
16° 
38° 
9° 
15 mm. 
8 
28% 
I 
2 
3 
4 
27° 
52° 
27° 
29° 
30° 
15° 
8 " 
17-5 " 
20 " 
17-5 " 
I 
77° 
71° 
35° 
25° 
13 " 
9 " 
40% 
I 
2 
3 
4 
32° 
41 
36° 
21° 
23° 
18° 
20° 
16 " 
18 " 
17 " 
10 " 
2 
68° 
89° 
37° 
23° 
13 " 
10 " 
20% 
Mean 
45° 
27-5° 
13 " 
Mean 
49° 
23-5° 
11.5 " 
28% 
Mean 
41° 
16 " 
Mean 
74° 
30° 
II " 
40% 
Mean 
36° 
20.5° 
15 " 
Mean 
___77-5°_ 
30° 
11.5 " 
The flat form of the curvature in air and in loose sawdust or 
sphagnum and the increasing acuteness of the curvature as the latter 
medium is compressed might, if our observations extended no further, 
lead us to suspect the presence of some substance having a specific 
action upon the root by which the sensibility to the geotropic stimulus 
or the ability to react could be increased. The fact that media of 
such widely dififerent nature as sphagnum, moor turf and even horn 
meal influence the curvature of the root as does moist sawdust speaks 
conclusively against that possibility. Sawdust which has been re- 
peatedly washed with water is not altered in its effect upon the curva- 
ture of the root. 
In a less compact mass of such a material as moist sawdust or 
sphagnum, the gas exchange would be more active than when the 
medium was compressed. In the more compact mass of the medium 
