Francis Darwin. 
3 6 
is of interest is that his research laid the foundation of the 
belief that the tip is the geo-perceptive region whence an 
influence is transmitted to the motor machinery. Unfortunately 
this instructive experiment was overborne by the great authority 
of Sachs 1 who found that decapitated roots did not behave 
uniformly but curved in various directions. On the other hand 
Ciesielski’s work was fully confirmed in the Power of Movement in 
Plants? The well-known Fig. 195 in that work illustrates Ciesielski’s 
second result and also the fact that geotropism returns with the 
regeneration of the root-tip. 
It remained to discover the meaning of Sachs’ results. Twenty 
roots were obliquely decapitated 3 so that the incision made an 
angle of 70° with the axis of the organ, ten other specimens were 
cut at an angle of 45". They were then placed vertically and nineteen 
of the thirty became much distorted. This trial was made because 
it was thought that oblique amputation might act like lateral 
injury in the tip, which was known to produce curvature. It seems 
therefore possible that Sachs’ results were due to oblique amputa¬ 
tion. 
The theory that geoperception resides in the root-tip was at 
once attacked by Detlefsen, a pupil of Sachs, in a paper 4 which 
may be neglected, and by Wiesner. 5 This naturalist’s criticisms 
were made in the fairest and most courteous spirit and are in 
many ways of value. But in this particular instance they have no 
great force. He tried to show that geotropism failed to occur 
because longitudinal growth was checked by amputation. But it 
is inconceivable that a diminution of the growth-rate by 25 or even 
50 per cent, could do more than delay or diminish geotropism, it 
could not account for the entire absence of curvature. Wiesner’s 
argument was upset by the work of several observers who showed 
that the growth-rate may be greatly depressed without eliminating 
geotropism. In my experiments 6 the method was to split the root 
longitudinally, i.e., to injure the tip without removing it. The rate 
of growth of the split roots was to that of the decapitated ones as 
1 Arbeiten, III., p. 432. 
2 p. 523. 
3 Power of Movement, p. 528. 
4 Sachs’ Arbeiten, II. 
6 Das Bewegungsvermogen der Pflanzen, 1881, 
0 F. Darwin. Linn. Soc. J., XIX., 1882. See Kirchner, Ueber 
die Emptindlichkeit der Wurzelspitze, &c, Stuttgart, 1882. 
Also Brunchorst, B.d. Deutschen Bot. Ges. ii. 
