7 2 
Francis Darwin. 
statoliths. The same may perhaps he said of the crystals which 
fall to the bottom of certain cells among the higher plants. 
The second section of evidence for the statolith theory is of an 
experimental character, and here great care is needed, as will be 
seen in the following instance. 
I subjected Sctaria seedlings to a high temperature, and this 
caused the starch grains to disappear and at the same time the 
seedlings lost the power of curving geotropically. This seemed a 
hopeful fact, but fortunately it occured to me to test their heliotropic 
powers, and it turned out that these had also been lost. Thus the 
loss of the statoliths must be considered merely as a symptom of 
the injurious effect of high temperature, and not as the loss of 
sense organs. 
The same caution must be applied to certain experiments of 
Haberlandt. He found that plants of Linum growing out of doors 
in the early winter were not geotropic and had no statolith-starch. 
When brought into a warm room starch appeared and the power 
of geotropic curvature returned. Unfortunately the evidence that 
heliotropism was not simultaneously affected is not conclusive. 
The same must be said of Haberlandt’s experiments in which the 
endodermis was removed by an operation with the result that the 
plants so treated lost their geotropic capacity. 
Roots. 
As already pointed out roots form the most serious difficulty 
of the statolith theory. In the first place we have no absolutely 
convincing evidence of the localisation of geoperception in the root 
tip, so that it may be urged that it is useless to investigate their 
statoliths. Still it is necessary to give some account of the difficulties 
that meet us. 
Nemec shows (as others have shown) that a root, from which 
the tip has been cut, is no longer geotropic. Such roots recover the 
power as the wound heals, and what is especially interesting is that 
geotropism does not return with general symptoms of regeneration 
but with the actual appearance of statocytes. Nemec removed 
one millimetre from the roots of a number of V. faba seedlings: 
after fifteen hours some were found curving downwards, while others 
remained horizontal. On examining them microscopically it was 
found that the geotropic roots had statoliths, the horizontal ones 
had none. This seems at first sight good evidence for our theory. 
But a critic might say that the whole effect is one of shock which 
affects some roots more than others, and moreover that the 
