Nov. 6,1916 Freezing Point of Leaf Sap of Per sea americana 263 
EXPERIMENTAL METHODS 
The technique employed in determining freezing-point lowering was 
very simple. Fully matured but still normally green leaves were col¬ 
lected and frozen in an ice and salt mixture to facilitate the extraction 
of sap by pressing 1 in a small heavily tinned bowl under a powerful 
screw. The freezing-point lowering was determined by mesons of a 
mercury thermometer graduated to 0.01 of a degree centigrade in subdi¬ 
visions sufficiently large to allow of fairly accurate estimation to smaller 
fractions. The vaporization of ether or carbon bisulphid in a vacuum 
jacket was used in determining the freezing-point lowering. The results 
are expressed in terms of freezing-point lowering in degrees centigrade (A), 
corrected for undercooling by the usual formula. 
For those who prefer to think in terms of osmotic pressure the values 
of P are given from a published table. 2 Finally, for the convenience of 
those who wish to know the actual freezing point of the saps on the 
Fahrenheit scale, these values have been added (F). 
PRESENTATION OF CONSTANTS FOR THE THREE TYPES 3 
Mexican type. —Throughout the highlands of central and northern 
Mexico this type is very common.. Because of its superior hardiness, it 
has been extensively planted in several subtropical regions, most notably 
in California and Chile. It is known to have been planted in California 
as early as 1870. In Florida it has fruited as far north as Gainesville, 
but is not generally cultivated in any part of the State. It has been 
planted along the Riviera in southern Europe and has fruited in the open 
at Rome. In Algeria it has also been planted, though to a very limited 
extent. In the West Indies it is scarcely known. 
During the cold weather of January, 1913, in California trees of this 
type were reported to have withstood temperatures of 16 0 to 20° F. 
without injury. 
1. Quer6taro... A=i.ii, P= 13.3, F= 3 o.oo° 
Buds received from California, where the variety was introduced from Quer6taro, 
Mexico, in 1911. Cion 1 year old, on one branch of No. 4, Mexican stock. 
2. San Sebastian ...A=i.2o, P=i4.5, 29.84° 
Buds received from California, where the variety was introduced from Quer£taro, 
Mexico in 1911. One-year-old cion on Mexican stock, a branch of No. 4. 
3. Harman... A=i. 24, P=i5.o, F=29.77° 
Originated at Sherman, Cal., budded on a limb of 26713, West Indian type. Cion 
2 years old. 
4. Seedling.A-1.27, P=i5.2, F= 29.71 0 
Grown from seed of unknown origin. 
1 Gortner, R. A., and Harris, J. A. Notes on the technique of the determination of the depression of the 
freezing point of vegetable saps. In Plant World, v. 17, No. 2, p. 49-53,1914. 
2 Harris, J. A., and Gortner, R. A. Notes on the calculation of the osmotic pressure of expressed vege¬ 
table saps from the depression of the freezing point, with a table for the values of P for A=o.ooi * to A-2.999 0 . 
In Amer. Jour. Bot., v. 1, no. 2, p. 75-78. 1914. 
3 The numbers following the varietal names refer to the Inventory of the Office of Foreign Seed and Plant 
Introduction, Bureau of Plant Industry. 
