196 BOTANICAL GAZETTE [aance 
negatively to an angle of 90°. The last two, and perhaps some 1 
others, evidently curved, not because of the stream, but because — 
of their objection to the water environment, whatever this objec- 
tion may be. The relatively large number of positive roots, 
however, warrants us in concluding that this species is rheotropic. 
Of the Compositae only Helianthus annuus has been used. 
Forty seedlings have been tested for a period long enough to 
determine their rheotropism. The temperature was 21° to 239 
air, the velocity 50° to 1000™ per minute, the period 17 to 33 
hours. Twenty-eight roots bent positively, six negatively, and : 
seven were neutral. The roots bending positively did not attai 
as great an angle as those of Fagopyrum, less than one-half 
passing beyond 45°. The roots of Helianthus do not all a 
count for the 
The Cruciferae have furnished by far ri 
the study of rheotropism. Of the six species studied, five @ 
theotropic, only Nasturtium officinale showing it lf wholly ee 
ferent. The white mustard, the black mustard, the turnip, ue 
cabbage, and the radish, but especially the first and tf od 
these five, give splendid examples of rheotropic roots: 
» Whe Cruciferae tried produce straight roots in water. In 
_ seedlings used were from 2™ to 4™ in length baa Ce 
of the experiment. . oo 
Brassica alba is one of the best of the eight 
_ have been found rheotropic. In five experi eee 
revolving basins of water, in which fifty-one seedlings 
with a velocity of 50°™ to 1000™ per minute, 4 ae 
ture of 19° to 22°, and a period from 6 to 21 h 
a roots bent strongly positively, the majority bein 
__ many being go°. Six roots were neutral. This 
age of 88 and marks the white mustard as 4 T” 
_ plant for experiment. Its great heliotropic sensitiv™ 
@ that the experiments for rheotropism be carried 
Fig. 5 shows the curves obtained in one eX{ 
me 
