504 



J. ARTHUR HARRIS 



of the osmotic concentration exhibited by the foliage of the ligneous 

 forms upon which they find lodgment. Of course these figures are 

 only approximations, which will be somewhat modified by further 

 work, but they are based on sufficient data to justify the conclusion 

 that the epiphytic species of the rain forest are characterized by a 

 concentration of about one third to one half that of the ligneous terres 

 trial species. 



TABLE 5 



Comparison of Osmotic Concentration of Epiphytic Forms -with that of Ligneous 

 Terrestrial Species in the Montane Rain Forest 



In passing it may be worth while to point out that these results 

 have an important bearing upon theories of the origin of parasitism. 

 The suggestion has been made that epiphytism is the first stage 

 in the evolution of parasitism in the flowering plants. But all 

 of these most typical epiphytes are characterized by very low os 

 motic concentration in comparison with the ligneous species of the 

 same region, whereas the Loranthaceae of these forests have been 

 shown (Harris and Lawrence, 1916) to have generally higher concentra 

 tion of their tissue fluids than their hosts. Similar relationships have 

 been found to exist in desert Loranthaceae (Harris, 1918). 



Theoretically one of the best methods of comparison would be to 

 lay side by side constants for terrestrial and epiphytic members of the 

 same family. Unfortunately I have not been able to secure terrestrial 

 Orchidaceae from subtropical Florida. Determinations have been 

 published (Harris and Lawrence, 191 ya) for Jamaican species. Epi- 

 dendrum verrucosum, which we included in our first paper because we 

 always found it growing on the ground, although Fawcett and Rendle 



