226 MR. F, DARWIN ON THE CONNECTION 
Here we have the same effect as before obtained, namely, 
that the operation produces a great retardation in growth at first, 
from which the cut roots quickly recover and grow even more 
rapidly than the normal ones. Thus, taking the average growths 
and reducing those of the normal roots to 100, we have :— 
First period. Second period. Whole growth. 
Normal 4 100 100 100 
DUE uccide 69:5 133 118 
It would, perhaps, be fairer to leave out of account the first of 
the eut roots, which grew extremely vigorously, and the last of 
the normal ones, which grew badly. "We then get:— 
First period. Second period. Whole growth. 
Normal... 100 1 100 
KİNE eere sore 575 . 100 874 
Thus, even in this case, the growth of the cut roots during the 
second period of 192 hours was equal to that of the normal roots. 
Conclusion.—It seems to me impossible, in the face of the above 
experiments, to say, as Wiesner has done, that the loss of geotro- 
pism in the cut roots is proportionalto their diminished rate of 
growth *. 
Experiments with Split Roots.—I shall now show that, even if 
cutting off the tips of the roots greatly retarded their growth, it 
would be a false conclusion to suppose that such retardation 
could account for the loss of geotropism. 
Sachs has shown that roots may be split longitudinally and 
may nevertheless be geotropie T. If the root is split into a 
middle lamella (containing most of the vessels) and two side 
pieces, the middle portion will bend geotropically, if the root is so 
placed that the cut surfaces are vertical. He has elsewhere (p. 436) 
pointed out that splitting roots in ¢wo lamelle f retards the 
growth in a marked manner. These facts seemed to point to the 
conclusion that retardation of growth is not necessarily connected 
with loss of geotropism ; and I therefore made the following ex- 
* In those cases in which the rate of growth of the cut roots becomes greater 
than that of the normal ones after recovery from the effects of the operation, 
it would have been better if the cut roots had been observed for rather a longer 
period, to make sure that no geotropism occurred. But this is of no real 
.conseguence, as the effects of cutting off the tip are known from so many other 
observations. 
t Arbeiten, Bd. i. p. 470. 
t When split in three, he says that they grow “ very strongly." 
