98 l^e'^combe, Gravitation sensitiveness not confined to apex of root. 
for the cotyledons of Ävena and Fhalaris, tlie whole cotyledon 
being* sensitive, but tbe sensitiveness diminisbing from tbe apex 
downward. 
Tbe bypotbesis given will account for tbe growtb of a seed- 
ling from tbe form sbown in Fig. 1 to tbat in Fig. 2, and will 
acconnt for tbe continuation of tbe root in tbe form sbown in Fig. 
3 (wben tbe seedbngis kept in tbe horizontal position). Wben,bowever, 
a root is forced into tbe form sbown in Fig. 3, allowed to grow for 
some bonrs in tbat form and position, and tben removed to tbe 
klinostat, and so revolved as to nentralize tbe effect of gravitation, 
we migbt expect, accordingto Czapek^) tbe Stimulation previonsly 
indnced in tbe horizontal part of tbe elongating zone, if tbat were 
sensitive to gravitation, to prodnce a geotropic cnrve. Since no 
such effect is seen, Czapek assiimes tbat tbe part of tbe root 
Fig. 3. 
Seedling of Lupinus alhus in position 
of equilibrium. 
Seedling of Brassica alba after 
Stimulation in stream of water. 
posterior to tbe apical one to two millimeters must be insensitive 
to gravitation. 
But tbis conclusion is not tbe only possible bypotbesis. Tbe 
tendency to bend, prodnced by gravitation, may be pre- 
vented by tbe autotropism of tbe root. 
Referring to Czapek’s experiments witb tbe bent glass caps, 
it may be said tbat it is not necessary to nse such a means to 
secui’e a great angular difference between tbe direction of tbe 
longitudinal axes of tbe root-apex and of tbe part just bebind 
it. As Nemec^) bas seen, so every one wbo bas experimented 
witb root curvatures bas seen inverted ortbotropic roots bend 
over into a horizontal or oblique position and subsequently for 
days continue on in tbe same direction, tbo tbe tip all tbe time 
was bent down ward as sbown in Fig. 3. I bave seen roots of 
Brassica alha^ after curving upward into neaiiy a horizontal po- 
__ # 
q über den Nachweis der geotropischen Sensibilität der Wurzelspitze. 
(Jahrb. wiss. Botanik. XXXV. 1900. 313.) 
q Über die Wahrnehmung des Schwerkraftreizes bei den Pflanzen 
(Jahrb. wiss. Botan. XXXVI. 1901. 78.) 
