328 Life and Inmortality. 
from the tip, we should, however, remember that it is the tip 
that is sensitive to the contact of hard objects, causing the 
radicle to bend away from them, thus directing it along cer- 
tain lines in the soil where the least opposition interposes. It is 
again the tip that is alone sensitive, at least in some instances, 
to moisture, causing the radicle to bend towards its source. 
These last two kinds of sensitiveness conquer for a time the 
sensitiveness to geotropism, which, however, ultimately pre- 
vails. But thethree kinds most often come into antagonism, 
first one prevailing, and then the other. It would, therefore, 
be an advantage, perhaps a necessity, for the interweighing 
and reconciling of these different kinds of sensitiveness, 
that they should all be localized in the same group of cells 
which have to transmit the command to the adjoining parts 
of the radicle, necessitating it to bend to or from the source of 
the irritation. 
Though generally believed by authors that the modifica- 
tion of the upper or lower surfaces of a radicle, whereby 
curvature is induced in the proper direction, is the direct 
result of gravitation, yet there can be no question from all 
that has been said that it is the tip alone that is acted on 
and that transmits some influence to the adjoining parts, 
causing them to curve in a downward manner. Gravity, it 
would seem, does not act in a more direct way on a radicle 
than it does on any lowly-organized animal, which moves 
away when it feels some weight or pressure. 
When we consider what we have written, it is impossible 
not to be impressed with the resemblance between the move- 
ments of plants and many of the actions performed by the 
lower animals. With plants an astonishingly small stimulus 
suffices. One plant may be highly sensitive to the slightest 
continued pressure, while a closely-allied form just as highly 
sensitive to a slight momentary touch. The habit of moving 
at certain periods is inherited both by plants and animals; 
and other points of similitude have been specified. But 
the most striking resemblance is the localization of their 
