ABSORPTION OF WATER BY EPIPHYTES. 



221 



in a detachment of the most superficial parts of the bark, but not of tlie 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. — Aerial Roots of an Orchid epipJiytic upon the barli of the branch of a tree. 



substratum, it immediately ceases to develop clamp-cells, loses its ligulate shape, 

 and hangs down fi'om 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 



