288 J. ARTHUR HARRIS AND JOHN V. LAWRENCE 
now to the comparisons of the local habitats among themselves we 
note the following points which must be taken into consideration in 
the analysis of the data. 
The comparisons between the windward and the leeward exposures 
on the basis of the now available data may be expected to give a 
minimum rather than a maximum measure of the differences between 
them. This is true for three reasons. First, we have made the com- 
parison between the plants of the windward slopes and windward 
ravines taken together and two of the sub-habitats of the leeward slopes. 
Thus if there be measurable differences between the sap properties 
of the windward ravines and the windward slopes, the combination 
of the two will tend to minimize the differences which might have been 
obtained had it been practicable to deal separately with the properties 
of the saps of the windward slopes and ravines. Second, we have 
arbitrarily excluded a great number of forms which are apparently 
the most hygrophilous and are possibly characterized by an even 
lower osmotic concentration than are the species for which determina- 
tions are given in these pages. Had it been possible to free the mats 
or festoons of certain of the cryptogamic epiphytes from the super- 
ficial water with which they are so constantly saturated, without 
modifying the concentration of their tissue solutions by drying, we 
believe that a series of determinations falling almost if not entirely 
in the lower range of variation in osmotic concentration as shown by 
the available determinations might have been obtained. Third, to 
render the results from the Blue Mountain habitats as nearly as 
possible comparable with others which have been or are being in- 
vestigated we have excluded the Bromeliaceae, the Orchidaceae, with 
the exception of truly terrestrial forms, and some other phanerogamic 
epiphytes. There is, as far as we are aware, no a priori reason to con- 
sider that these forms would be characterized by low osmotic con- 
centrations. While the detailed discussion of these ecologically most 
interesting forms is reserved for a comparative study to be published 
later, it may be said in passing that the concentration of these forms 
has been found to be usually far lower than that of other species of 
the vegetation. 
These facts while they must detract somewhat from our constants 
as an exact description of the region in question, make differences 
secured under these limitations much more significant. 
In considering differences in sap concentration in relation to local 
