570 BOTANICAL GAZETTE [JUNE 
Osmotic concentration and habitat.—The influence of habitat and environ- 
mental conditions upon the sap concentration of leaf cells has received con- 
siderable attention recently from Harris and his co-workers. The cryoscopic 
method has been used in all determinations of the concentration of tissue fluids, 
and the studies have now become sufficiently extensive to permit comparisons 
between the average conditions found in plants of different regions. "The man- 
grove vegetation of Jamaica and Florida" has been examined with reference 
to the influence of salinity of soil water on leaf sap concentration. Three 
species belonging to three different families were used. The sap concentration 
is high in all of them, 25-50 atmospheres. Avicennia nitida develops the 
highest concentration of the three, but shows the least variation with environ- 
ment. Rhizophora mangle gave freezing point depressions equivalent to 22-30 
atmospheres, and showed distinctly lower leaf sap concentration in fresh water 
habitats. Laguncularia racemosa responded most noticeably, with about 20 
atmospheres in fresh water, 25 atmospheres in normal sea water, and 33 atmos- 
pheres on sterile mud flats where the sea water is concentrated by evaporation. 
A similar study has been made of the Jamaican Blue Mountain rain forest 
vegetation,” where the rainfall averages from 100-130 inches per year. Only 
terrestrial plants have been reported upon so far, coming from four distinct 
sub-habitats: the ruinate of leeward slopes, leeward ravines, ridges, and wind- 
ward slopes and ravines. The plants of each habitat are grouped as ligneous 
and herbaceous. Distinct differences in the concentration of the tissue fluids 
of plants growing in each habitat were found, and, as in previous work, the 
ligneous plants of each type habitat proved to have more concentrated leaf 
sap than the herbaceous group. e average osmotic concentration of the 
ligneous plants is about 11.44 atmospheres, and of herbaceous plants 8.8 atmos- 
pheres. These figures are lower than for any region thus far investigated, and 
contrast strongly with values obtained from our southwestern deserts, where 
herbaceous plants reach 15 atmospheres and ligneous plants 25. In ascending 
order of sap concentration, the four sub-habitats stand as follows: the wind- 
ward slopes and ravines, leeward ravines, ridge forests, and ruinate. 
Variation in leaf sap concentration with height of insertion on the tree* 
has been studied also, and Drxon’s results confirmed, that the concentration 
of sap is almost always higher, the higher up the leaf is on the tree. Since, 
however, the specific electrical conductivity of the sap usually decreases from 
lower to higher levels, it is probable that photosynthetic sugars are produced 
x aie J. AntHuR, and Lawrence, Joun V., The osmotic concentration of the 
sap of the leaves of mangrove trees. Biol. Bull. 32:202-211. 1917 
12 
The osmotic concentration of the tissue bases of Ser. montane 
rain forest vegetation. Amer. Jour. Bot. 4:268-298. 19 
*’ Harris, J. ARTHUR, GoRTNER, Ross AIKEN, pie Lawrence, Joun V., The 
relationship between the osmotic concentration of leaf sap and height of leaf insertion 
in trees. Bull. Torr. Bot. Club 44:267-286. 1917. 
