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 (Sarcajithus rostratus) assuming the form of straps. 



selves, besides, by means of special aerial roots which hang down in white ropes 

 and thi-eads, 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 



