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.— Aerial Roots of an Orcliid epiphytic upon the bark of the branili 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, 



