320 Pfeffer . — Geotropic Sensitiveness of the Root-tip. 
revolve slowly about their own axis on a klinostat, while 
they were growing into the tubes. If now a specimen thus 
prepared is placed so that the terminal part points vertically 
downwards, whilst the rest of the root is horizontal, no 
geotropic curvature takes place. This, however, always took 
place, and with about the same promptness as in straight 
roots, when the terminal portion was directed horizontally, 
or in general at an acute angle with the normal position. 
From these experiments it follows that the root thus 
treated is perfectly capable of reaction. A geotropic reaction, 
however, only follows when the tip of the root is not placed 
in the position of equilibrium, that is when it is inclined from 
the vertical. But if the tip is directed vertically downwards, 
the rest of the root may occupy the horizontal or any other 
position, without any geotropic reaction following. 
By this means therefore it is proved with the most perfect 
certainty, that in an uninjured root only the root-tip is 
geotropically sensitive. 
