ABSORPTION OF WATER BY EPIPHYTES. 221 
in a detachment of the most superficial parts of the bark, but not of the tubular 
cells. Now, if a root, after having sent out cells of this kind which contract an 
organic union with the substratum, reaches into the open, beyond the limit of the 
Fig. 50.—Aérial Roots of an Orchid epiphytic upon the bark of the branch of a tree. 
substratum, it immediately ceases to develop clamp-cells, loses its ligulate shape, 
and hangs down from the tree in the form of a sinuous white filament. A few 
root-fibres are as a rule sufficient to fix the plant to its substratum, the bark of the 
tree, and the rest of the roots put forth by the orchid grow from beginning to end 
