Newcombe, Gravitation sensitiveness not confined to apex of root. 9? 
of tlie perceptive organ to the part excised; for it has been thought 
that the wounding miglit destroy the sensitiveness of tbe elonga- 
ting Zone posterior to the woimd. By the ingenious employment 
of glass caps bent at a right angle into which the roots were 
forced to grow, Czapek was able to cause the apical one and 
half millimeters of the root to take an angle of 90 o with the 
rest of the root; and thus one region of the root could be placed in 
its Position of equilibrium with regard to gvavitation, while the other 
region was 90 ^ removed from this position. 
If the seedling with the glass cap over the apex of the root 
was set up as shown in Fig. 1, in a short time it had changed 
to the relations shown in Fig. 2. If the seedling was laid hori- 
Fig. 1. 
Seedling of Lu'pinus albus with glass 
cap over root-tip. After Czapek. 
Seedling of Lupinus albus after the root 
has taken its position of equilibrium. 
zontally as in Fig. 3, it continued to grow without changing the 
Position of tip or elongating zone. 
These results were interpreted to mean that only the apical 
one or two millimeters of the root was sensitive to gTavitation. A 
moment of reflection will show that the results accord with an 
entirely different hypothesis. Suppose merely that in Fig. 1 the 
horizontal 2 mm of the root-tip is more sensitive to gravitation 
than the elongating zone above it; then the root wül swing into 
or toward the position shown in Fig. 2. If the apical 2 mm are 
much more sensitive than the adjacent older part, the tip may 
attain the vertical position as shown in Fig. 2, whoUy overcoming 
the effect of the sensitiveness of the elongating zone. Such a 
distribution of sensitiveness to hght has been made out by Bothert i) 
9 Über die Fortpflanzung des heliotropiscben Reizes. (Ber, d. d. bot. 
Gesellsch. X, 1892. 374.) 
Beihefte Bot. Centralbl. Bd. XXIV. Abt. I. Heft 1. 
7 
