« 
502 J. ARTHUR HARRIS 
the Piperaceae. The number under each of the averages is the number 
of species, not the number of determinations, upon which it is based. 
The averages for terrestrial herbaceous species are those already 
published (Harris and Lawrence, 1917a). 
The general mean for the region has been computed by averaging 
the species means for the individual habitats. Thus if a species 
occurs in both the Leeward Ravines and the Ridge Forest it is counted 
twice, whereas the species which occur in one of these habitats only 
will be counted but once. Thus the numbers of the species given for 
all habitats is the number of species weighted with the number of the 
sub-habitats in which they occur. ^ 
The comparison between the epiphytic and the terrestrial* her- 
baceous forms has been made in two ways. First, the actual differ- 
ences in the average depression of the freezing point and in the average 
calculated osmotic concentration have been determined and are given 
with their signs. Second, the average values of P of the epiphytes 
have been expressed as a percentage of the value for terrestrial herbs.'^ 
An examination of the nine comparisons between the epiphytic and 
terrestrial herbs of the four individual habitats shows that the con- 
centration is in every instance lower for the epiphytic forms. The 
averages are roughly 4.0 to 5.4 atmospheres lower in the Orchidaceae, 
3.8 to 5.2 atmospheres lower in the Bromeliaceae, and 3.4 to 3.6 atmo- 
spheres lower in Peperomia of the Piperaceae.^ 
There now remains for consideration only the half shrubby ges- 
neraceous epiphyte Columnea hirsuta. One determination from the 
Leeward Ravines gives A = 0.395, P = 4-7^- Eight constants from 
the Windward Slopes and Ravine average A = 0.354, P = 4.28. If 
these be compared with the averages for herbaceous vegetation from 
the same habitats, differences in P of —2.83 for the Leeward Ravine 
determination and of —3.24 for the Windward habitats are secured. 
^ This method of computing the average has both advantages and disadvantages. 
For present purposes it is quite adequate. 
^ Practically the same percentages are secured by using the average values of 
freezing-point lowering, but since the relationship between A and P is not strictly 
linear the results are not exactly identical. 
* Comparisons with the herbaceous plants of the regions as a whole show a 
concentration 5.1 atmospheres lower for Orchidaceae, 4.5 atmospheres lower for 
Bromeliaceae, and 4.2 atmospheres lower for Peperomia of the Piperaceae. The 
averages for the whole region is obtained by weighting those of the individual habitats 
with the number of species examined. 
