1902] THE RHEOTROPISM OF ROOTS 277 
stimulus, such as that given by a water current of a few centi- 
meters per minute, gives an average angle in Brassica alba and 
Raphanus sativus of perhaps 15°, while the most favorable stimulus 
brings a response averaging nearly go°. 
It might be thought that a root responding to the rheotropic 
stimulus by producing an angle of 45° to 90° from its direction 
of geotropic equilibrium would soon show signs of fatigue by the 
reduction of this assumed angle. Such behavior, however, on 
the part of the plant has not been observed, in cases where the 
stimulus is above a relatively low intensity and below a relatively 
high mechanical pressure. Thus, ten roots of Zea mays (everta), 
‘In velocities ranging from 50°™ to 100™ per minute, all attained 
Mangle of 45° in 11 hours, and maintained the same angle to 
the end of the experiment, 10.5 hours later. Aelianthus annuus, 
os with ten roots in water flowing 100° to 500 per minute, showed 
: Les foots retaining their angle of go0°, 33 hours after the begin- 
: ae of the €xperiment, this angle having been attained by most 
3 tthe roots 15 to 18 hours earlier. Ten seedlings of Raphanus 
. es ‘(variety Yellow Oval) all bent their roots positively in a 
* leg 350% to 400 per minute, temperature of water 23°, 
i oie between twelve and eighteen hours, the exact time 
he fo sttved. The angles attained varied from 15° to 90°. | 
“a a hours after beginning the experiment all roots were — 
ioe ve and at angles of 30° to go°. A set of seven seed-— 
lings of the Earl 
4 po ol the experiment, twenty-nine hours after the angles 
Wt appeared 
+fthe Current is ver 
wiki y weak many instances have been observed 
ae raightens into its vertical position after an_ 
.. ergs curve. Four Toots of Avena sativa growing 
ie i ent velocities ranging from 50° to 100% per - 
stall straigh se wtVelY theotropic within the first 334 hours, 
wentened within the ensuing 114 hours. Brassica alba 
: -~prer : : . ee ee 
© to, ah Paration in a revolving basin where the velocities for 
| "testa See from 50° to 100™ per minute showed SIX 
o 89 within three hours, but within the next hour four 
y Long Scarlet radish held their positive angles bs 
