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 
Habitats 
Average 
for 
Ligneous 
Plants 
Difference and Relative Value 
Orchidaceae 
Bromeli- 
aceae 
Piperaceae 
Gesneraceae 
Ruinate of the leeward slopes. . . 
Leeward ravines 
Ridges and peaks 
Windward slopes and ravines . . . 
13-05 
(w=4o) 
10.83 
(w=32) 
11-54 
(«=36) 
. 9-73^ 
(n=28) 
-7-43 
31.4% 
-8.32 
27-9% 
-6.23 
36.0% 
-8.45 
35.2% 
-7.89 
31.6% 
—6.00 
38.3% 
-6.60 
39-1% 
-6.35 
45-0% 
-5-75 
40.9% 
— 6.07 
44.0% 
-5.45 
44-0% 
All habitats 
11.44 
(« = I36)- 
-8.07 
29-5% 
-7-48 
34.6% 
-7.21 
37-0% 
-7.11 
37.8% 
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, 191 6) 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, 1917a) 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 
