98 Newcombe, Gravitation sensitiveness not conflned to apex of root. 



for tlie cotyledons of Avena and Ehalaris, the whole cotyledon 

 belüg sensitive, but the sensitiveness diminishing from the apex 

 downward. 



The hypothesis given will acconnt for the growth of a seed- 

 ling from the form shown in Fig. 1 to that in Fig. 2, and will 

 account for the continuation of the root in the form shown in Fig. 

 3 (when the seedlingis kept in the horizontal position). When,however, 

 a root is forced into the form shown in Fig. 3, allowed to grow for 

 some hours in that form and position, and then removed to the 

 klinostat, and so revolved as to neutralize the effect of gravitation, 

 we might expect, accordingto Czapek 1 ) the Stimulation previously 

 induced in the horizontal part of the elongating zone, if that were 

 sensitive to gravitation, to produce a geotropic curve. Since no 

 such effect is seen, Czapek assumes that the part of the root 



Fig. 3. Fig. 4. 



Seedling of Lu/pinus albus in position Seedling of Brassica alba after 



of equilibrium. Stimulation in stream of water. 



posterior to the apical one to two millimeters must be insensitive 

 to gravitation. 



But this conclusion is not the only possible hypothesis. The 

 tendency to bend, produced by gravitation, may be pre- 

 vented by the autotropism of the root. 



Referring to Czapek's experiments with the beut glass caps, 

 it may be said that it is not necessary to use such a means to 

 secure a great angular difference between the direction of the 

 longitudinal axes of the root-apex and of the part just behind 

 it. As Nemec 2 ) has seen, so every one who has experimented 

 with root curvatures has seen inverted orthotropic roots bend 

 over into a horizontal or oblique position and subsequently for 

 days continue on in the same direction, tho the tip all the time 

 was bent downward as shown in Fig. 3. I have seen roots of 

 Brassica alba, after curving upward into nearly a horizontal po- 



*) Über den Nachweis der geotropiscben Sensibilität der Wurzelspitze. 

 (Jahrb. wiss. Botanik. XXXV. 1900. 313.) 



*) Über die Wahrnehmung des Schwerkraftreizes bei den Pflanzen 

 (Jahrb. wiss. Botan. XXXVI. 1901. 78.) 



