576 A TEXTBOOK OF BOTANY [Ch. XIV 



roots, as in English Ivy (Fig. 180), or at the ends of modified 

 tendrils, as in Boston Ivy. 



B. The Habitats occupied by Epiphytes. 



The horizontal branches of trees, which spread their own 

 foliage so well to the light, offer opportunity for a spread of 

 foliage by other plants also. Correspondingly there occur 

 many small plants which grow on the branches and trunks 

 of trees far above the ground, especially in tropical forests ; 

 and such are the typical epiphytes. The epiphytic is the 

 logical development of .the climbing habit. The situa- 

 tion involves difficulties, — viz. the seeds must reach the 

 branches and germinate there, the plant must hold securely 

 to the slender perch, the roots must acquire the needed min- 

 eral salts and water without contact with the ground. The 

 epiphytes, however, show ample fitness to all of these condi- 

 tions in adaptations which are often remarkable. The 

 seeds are carried chiefly by birds; the plants are firmly 

 anchored by roots insinuated into the crevices of the bark; 

 mineral salts are obtained from a humus resulting from 

 decaying bark, leaves, etc., collected by the plant; water is 

 derived from the rainfall, absorbed and stored in various 

 ways, though the limitations and inconstancy of such 

 sources have evolved xerophytic adaptations which con- 

 serve it. 



The epiphytes include members of all the great divisions of 

 plants — Algae, Fungi, Liverworts, Mosses, Ferns, and 

 various Spermatophytes. Also epiphytes occur in the water 

 upon hydrophytes, as do parasites. The principal vege- 

 tation forms are the following. 



Orchidaceous Epiphytes ; with storing pseudobulbs, and 

 hanging aerial roots fitted to absorb rainfall (page 254 ; Fig. 

 126). Tank Epiphytes; funnel-form rosettes of leaves, 

 forming a cup which holds water, as in JEchmea (Fig. 127). 

 Water reservoirs of other forms are also frequent. Nest 

 Epiphytes; with certain leaves so arranged as to catch 



