574 Darwin . — Localization of the Sensitive Region . 
soon as a stem or root begins to curve the line of gravitation 
strikes it at a new angle, and therefore the stimulus is not 
constant. But with Setaria or Sorghum the sensitive part 
remains in one position, so that the stimulus is constant. 
I have made a number of experiments with grass seedlings at 
various angles, but I have not been able to come to a definite 
conclusion, although the result certainly favours the belief 
that a seedling fixed with the cotyledon pointing obliquely 
downward is more strongly stimulated than when it is in 
the opposite position 1 . 
The method which I have described I hope to apply to 
a number of other plants, especially those in which sensitive- 
ness to light is known to be only partially localized at 
the apex. 
I have already tried it with leaves and with diageotropic 
flowers, but the results are not yet complete enough for 
publication. 
1 Miss Pertz has tested this point by means of the intermittent klinostat without 
being aware that Czapek had used this method. With grass-haulms she obtained 
results similar to Czapek, and there can be no doubt that his result is correct. 
See Miss Pertz’s communication in the present number of the Annals of 
Botany, p. 620. 
DESCRIPTION OF FIGURES IN PLATE XXIX. 
Illustrating Mr. Darwin’s paper on Geotropism. 
Figs. 1 and 5. Setaria'. seven days’ exposure. 
Figs. 3 and 4. Sorghum : six days’ exposure. 
Fig. 2. Phalaris ; ten days’ exposure. 
For further details see p. 57 r. 
