SAPROPHYTES IN WATER, ON THE BARK OF TREES, AND ON ROCKS. 107 
always seen torn off with the rhizoids at the places where they issue from the 
stemlets. The same thing occurs in the case of the roots of tropical orchids 
growing to the tree-trunks which constitute their habitat. The majority of these 
tree-orchids nestle, no doubt, in mould-filled crevices of the bark, and nourish them- 
Fig. 15.—Aerial Roots of a Tropical Orchid (Sarcanthus rostratus) assuming the form of straps. 
selves, besides, by means of special aerial roots which hang down in white ropes 
and threads, like a mane, from the places where the plants are situated upon the 
trees, and which will presently be described in detail. But a small section develops 
strap-shaped roots as well, which adhere firmly to the bark with their flat surfaces. 
This phenomenon is most strikingly exhibited by the splendid Phalcenopsis 
