JOURNAL OF AGRMIim RES EARC H 
DEPARTMENT OF AGRICULTURE 
Von. VII Washington, D. C., November 6, 1916 No. 6 
FREEZING-POINT LOWERING OF THE LEAF SAP OF THE 
HORTICULTURAL TYPES OF PERSEA AMERICANA 
By J. Arthur Harris, Investigator, Station for Experimental Evolution, and Wilson 
PopEnoE, Agricultural Explorer, Bureau of Plant Industry 
INTRODUCTION 
In the introduction of tropical economic plants into the warmer por¬ 
tions of the United States, which for the most part are not free from at 
least occasional frosts, ability to survive transient low temperature is a 
characteristic of such fundamental importance that any quantitative 
contribution to our knowledge of its physiology must be of value. Among 
the factors to which frost resistance in plants is due, the magnitude of 
the depression of the freezing point of the cell sap has been suggested as 
one of importance. 
That the freezing-point lowering of the cell sap is not in itself a suffi¬ 
cient explanation of differences in frost resistances should be quite 
obvious from the narrowness of its range in plants of economic importance. 
To what degree the osmotic pressure of the sap may be correlated with 
other characteristics which are of significance in cold resistance remains 
to be investigated. 
A discussion of the several possible factors or references to the very 
extensive literature of the subject fall quite outside the scope of a note 
which is designed only to present a series of constants pertinent to the 
problem of hardiness in a particular tropical fruit. 
The Plant Introduction Field Station at Miami, Fla., has seemed to 
the writers to afford particularly advantageous materials for a test of 
the existence of a relationship between capacity for cold resistance and 
the freezing-point lowering of the extracted sap, since it contains, 
assembled under the same environmental conditions, a wider range of 
varieties than can be found elsewhere. 
The avocado, Per sea americana Miller (Per sea gratissima Gaertn. f.), 
while introduced to Florida and California a good many years ago, has 
only been propagated asexually since the beginning of the present 
century. Hence, the number of horticultural varieties is not over¬ 
whelmingly large. Some of these varieties have been under observation 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C 
fy 
(261) 
Vol. VII, No. 6 
Nov. 6,1916 
G-98 
