276 BOTANICAL GAZETTE | APRIL 
rheotropic latent period, both considered without the neutraliza- 
tion of the effect of gravitation. Roots of Raphanus sativus 
rheotropically curved have been seen to begin to straighten 
geotropically 20 minutes after the water stream was stopped, 
the temperature in air being 23°. Under similar conditions, 
except at an air temperature of 28°, the roots of Zea mays 
(everta) began to straighten geotropically in 40 minutes. On 
the other hand, two roots of Vicia faba, at a temperature of 25° 
in air, continued to bend rheotropically for an hour after the 
water stream was stopped. 
From the foregoing results we may conclude that the rhe: 
otropic stimulus is in active competition with the pees 
stimulus, so that the operation of the latter is very quickly 
manifested when the former ceases to operate. One might have 
supposed the after-effect would have been considerably pro 
tracted, seeing that the latent period is so long. Such, however, 
is not the case. It remains an open question whether the 
rheotropic latent period would be greatly shortened — x 
opposing geotropism eliminated. The latent period . a : 
response is no greater than that for traumatropism ‘and that ae 
_ the clasping of some tendrils.” ee 
IV. PERSISTENCE OF SENSITIVENESS. ; 
f water is continuous Ove 
dence to show 
The response of roots to a stream 0 
a long period; and although there is some ¢v! 7 
: _ that roots subjected to a rheotropic stimulus lose 17 ees 
their geotropic sensitiveness, yet we may regard pag eee . 
taken by the roots growing in a stream of water ei } 
direction. This resultant direction forms a greater . 
I 
90° in Fagopyrum esculentum, Raphanus sativus, 4 
other plants, or it may average no more than 45 
V. sativa, Pisum sativum, and Helianthus annuus. * —* 
annals of Boas 
Aver 
“SPALDING: On the traumatropic curvature of roots. 
f Darwin: The movements and habits of climbing plants. 
