Nov. 6,1916 Freezing Point of Leaf Sap of Persea americana 267 
An inspection of the values in Table I shows no clear difference between 
the plants of the Guatemalan and Mexican types. From both of these 
the West Indian type seems to be differentiated by a distinctly slighter 
freezing-point lowering. All but 3 of the 17 West Indian determinations 
are lower than 1.20 0 , whereas all but 4 of the 22 based on plants of the 
Guatemalan and Mexican types show a freezing-point lowering of 1.21° 
or more. 
If the averages of the freezing-point lowerings (A) with their probable 
errors be determined as a more exact means of comparison from the 
ungrouped depressions given for the individual varieties above, the 
following constants are obtained (Table II). 
Table II.— Freezing-point lowering constants of three types of Persea americana 
Type. 
Mean. 
Standard 
deviation. 
. Coefficient 
of variation. 
Guatemalan. 
1. 304 ±0. 024 
1. 3°5 ± -0i6 
1* 305 ± .014 
1. 096 ± . o'i4 
O. 106 ±0, 017 
. 087± • 012 
. 095 ± .014 
. 0831b . 010 
8. 16 
Mexican. 
6. 68 
Guatemalan and Mexican. 
7 - 2 $ 
7 - 55 
West Indian. 
The average freezing-point lowering in the Guatemalan and Mexican 
types is practically the same. The difference is only 0.001 ±0.029 °f a 
degree. The West Indian type is characterized by a distinctly lower 
average than either of the other types. The differences are: 
West Indian and Guatemalan type. — o. 209 ±0. 027 0 
West Indian and Mexican type. — o. 210 ±0. 021 0 
West Indian and Guatemalan and Mexican types. — o. 209 ±0.019° 
These differences are 7.6, 9.9, and n times as large as their probable 
errors. Thus, notwithstanding the relatively small number of observa¬ 
tions upon which this study has of necessity been based, the differences 
seem to be quite trustworthy in comparison with their probable errors. 
Within the type the absolute variation in freezing-point lowering is 
very slight, amounting to one-tenth of 1 degree or less. The relative 
variability as expressed in terms of the coefficient of variation is also 
low for a plant character. 
SUMMARY 
The constants presented in this paper prove that in a tropical fruit 
of relatively recent introduction to North American horticulture, the 
avocado, one of the groups of varieties, the so-called West Indian type, 
is characterized by tissue fluids which freeze at a distinctly higher tem¬ 
perature than in the two other groups of varieties (Guatemalan and 
Mexican). In the conventional terms of physical chemistry adopted by 
physiologists, the expressed leaf sap of West Indian type varieties is 
characterized by a slighter depression of the freezing point or by a 
slighter freezing-point lowering than is that of the two other groups of 
