OSMOTIC CONCENTRATION OF TISSUE FLUIDS 29"^ 
of growth forms is clearly marked in the series of determinations from 
each of the Blue Mountain habitats. The differences are not, how- 
ever, so large as those demonstrated in the desert series. 
The four sub-habitats, recognized in the Blue Mountains, show 
distinct differences in the osmotic concentration of their tissue fluids. 
The ruinate, which has been regarded by ecologists as the most 
xerophytic of the habitats, shows a distinctly higher osmotic con- 
centration of the leaf tissue fluids of its constituent species than 
any other habitat. The plants of the ridge forest show a higher 
osmotic concentration than do those of the leeward ravines and the 
windward ravines and slopes, but lower than that of the plants of the 
ruinate. The leeward ravines are characterized by plants with lower 
osmotic concentration than the vegetation of the ruinate and of the 
ridge forest, but higher than that of the windward ravines and slopes. 
Finally, the windward habitats, which are the most hygrophilous of 
the region, are characterized by a sap concentration lower than that 
of any other habitat. 
The osmotic concentration in the sap of the plants of the Blue 
Mountains is the lowest of that of any region as yet extensively 
investigated. The ligneous forms show an average concentration 
of about 11.44 atmospheres as compared with 14.96 atmospheres in 
Ohlweiler's St. Louis series and 14.40 for our own preliminary series 
from Long Island habitats. The average concentration for herbaceous 
plants in the Blue Mountains is about 8.80 atmospheres as compared 
with 10.41 atmospheres from our preliminary Long Island series. 
Comparisons with desert regions show much more striking dif- 
ferences. Thus the herbaceous plants of the rain forest show an 
average concentration of 8.80 atmospheres as compared with 15.15 
atmospheres in the herbaceous plants of the winter flora of the deserts 
around Tucson. The ligneous plants of the rain forest have a con- 
centration of only about 11.44 atmospheres as contrasted with 24.97 
atmospheres in the series of ligneous plants investigated in our south- 
western deserts. The Jamaican coastal deserts show slightly higher 
concentration even than those of the Arizona series. 
While these general averages are the simplest expression of the 
differences between these regions, they are by no means an adequate 
description. They conceal the differences which obtain in each of 
the areas investigated. For a more adequate conception of the 
conditions, the reader must turn to the more detailed comparisons 
