| CRYOSCOPIC DETERMINATIONS ON TISSUE FLUIDS 
OF PLANTS OF JAMAICAN COASTAL DESERTS! 
J. ARTHUR HARRIS AND JOHN V. LAWRENCE 
Introduction 
PURPOSE OF STUDY.—In a memoir recently published? we have 
discussed in detail the reasons for considering the physico-chemical 
properties of vegetable saps a subject of real importance in ecology . 
and phytogeography, and have reinforced the arguments advanced 
by series of determinations showing distinct differences in the 
osmotic pressure, or osmotic concentration, as some prefer to call it, 
of leaf sap from plants growing in different local habitats in the 
Arizona deserts. A comparison of these determinations with a 
series made in the more mesophytic region of the Station for 
Experimental Evolution? demonstrated a conspicuous differentia- 
tion of the Tucson and Cold Spring Harbor regions with respect to 
the osmotic concentration of the tissue fluids of the constituent 
species. In view of the s diff tablished between 
these two floras, it seemed desivable to select a forested region of as 
uniformly distributed and as nearly maximum rainfall as possible — 
for comparison with the areas already studied. Thus we hoped to 
3 the iohtaha tals force ol the asad of Tenis wey de | 
by Sureve,* seemed the most suitable locality. ‘We therefore 
spent a period of several uring t eae ree 
