410 VEGETABLE PHYSIOLOGY 
from the wound and a new root-tip was developed upon each. 
As soon as the new tip was formed, the rootlets showed a 
power of reacting to the stimulus of gravitation, and the 
curvature resulted in the usual place. If we turn to the 
reaction of the leaf of Dionwa to contact, we find that tke 
whole leaf may be somewhat roughly handled without 
Closing, so long as no contact is made with the hairs, three 
in number (fig. 160), which arise upon a particular portion 
Fia. 160.—Lrar or Dionewa muscipula. 
1, open; 2, closed: a lateral view, b, surface view; 3, one of the sensitive 
spines ( x 50); 4, glands on the surface of the leaf ( x 100). 
of the blade. So soon, however, as one of these is touched, 
the leaf closes. 
In many leaves the cells of the upper epidermis are convex 
on their upper surfaces, and a ray of light passing through 
them is brought to a focus somewhere in the palisade par- 
enchyma, with such distinctness that it is possible to use 
a piece of detached epidermis in the fashion of a number 
of lenses placed side by side. Haberlandt has attributed 
a perceptive function to these cells, which he calls ocelli. 
