266 MR. F. DARWIN ON A METHOD OF INVESTIGATING THE 
On a Method of Investigating the Gravitational Sensitiveness of 
the Root-tip*. By Francis Darwin, M.B., F.RB.S., F.LS. 
[Read 6th February, 1902.] 
Tue theory put forth in the ‘Power of Movement in Plants,’ 
that the tip of the root is the part of that member which is 
sensitive to gravitation, has gone through some vicissitudes which 
it is needless to recapitulate. It is sufficient to refer to the 
most recent development of the subject. Since the appearance 
of Pfeffer’s t and Czapek’s ¢ papers, physiologists have, broadly 
speaking, agreed that the long-desired proof has been supplied. 
But no confirmatory experiments were published, while, on the 
other hand, the work of Wachtel § gave a direct contradiction to 
Czapek’s paper. Last year we had Czapek’s able reply ||, which 
shows that Wachtel’s contradictory results depend on a difference 
in the manner of making the bent tubes used in the experiments. 
In this position of the question a confirmation by another 
method is desirable ; and this is what I have tried to give in the 
following paper, which is an application to roots of the method 
successfully employed with Setaria and Sorghum, &c. J 
A seedling of one of these grains, e.g. Sorghum, when prepared 
for use by the removal of the root, consists of the grain and 
the straight hypocotyl surmounted by the cotyledon, shaped like 
a spear-head. If such a seedling is supported by means of the 
grain (S in fig. 1) in a horizontal position, the hypocotyl bends 
upwards until the cotyledon C is vertical, and the further 
growth is in the vertical direction. But if the cotyledon is 
supported as in figs. 2 and 3, the ‘part of the plant which is 
sensitive to the gravitational stimulus remains horizontal, and 
therefore continues to perceive tbe stimulus, and the curvature 
of {the hypocotyl therefore continues. In this way coils and 
spirals in the hypocotyl are formed even more complex than 
those shown in figs. 2 and 3. 
‘901 brief note on this subject was published in Proc. Cambridge Phil. Soc. 
+ Pfeffer, Annals of Botany, 1894, 
{ Czapek, Pringsheiin’s Jahrbicher, 1895, 1898. 
§ Wachtel, Bot. Zeitung, 1899. 
| Czapek, Pringsheim’s J. ahrbiicher, 1900, 
“| Francis Darwin, Annals of Botany, 1894), 
