AGRICULTURAL METEOROLOGY. 129 
example, perhaps freezes to the point of being filled with orystals of 
ice entirely without injury. The reverse is observed with some plants 
apparently very strong, like the acacias of New Holland, which are 
very susceptible to the frost. In the other plants the quantity of water 
contained in their cells may serve as an indication. The wood of the 
sane species of tree admits also of different conditions in spring, ac- 
cording to the state of the juices which it contains. The almond tree, 
situated in a sheitered position, and exposed to the sun, frequently per- 
ishes, while that planted upon the slope of a hill escapes from the frost. 
Sheltered positions, which are in sammer and autumn favorable to the 
development of fruit, are disadvantageous in spring, on account of the 
acceleration which they often impose upon vegetation. At the close of 
the winter of 185455, thousands of almond aud peach trees perished 
by the frost in the neighborhood of Frankfort, and those in the enclos- 
ures sheltered from the north, and uncovered toward the south, suf- 
fered the most. The same fact was observed at Giessen. 
Hoffmann says there does not exist any general rule by which to fix . 
in advance the point to which a plant, or an organ, will resist the frest. 
We have for guidance in this regard only isolated observations.. We 
cannot explain why plants, or parts of plants, sometimes delicate, and 
sometimes solid, do not suffer from the frost. But Hoffmann believes 
that he has proved why certain plants do suffer. i give his theory. 
If we expose the leaves of rosemary, camellia, &c., to a cold of fron 
10° to 20° ©. below zero, we do not remark any alteration at the end of 
several days; but if the sun touches the leaves in such a manner that 
their temperature is elevated for one moment above zero, so as to cause 
thawing, they undergo the most considerable alterations; the plants 
fade with all the symptons of being entirely withered, and the leaves 
appear dry in a temperature of 50° to 68° C. above zero. The same 
phenomenon is produced when we place the frosted leaves in an enclos- 
ure without the sun, and where the temperature is only six-tenths of a 
degree above zero; thus the rapid increase of temperature is not the 
sole cause of these alterations. We may save parts of plants which are 
frozen by the sprinkling of cold water; it has been believed that this 
effect is due to the slowness of the thaw thus produced, but this 
opinion is erroneous, for the water renders the same service when it is 
warm. Hofitmann has several times observed that the leaves of Cam- 
phora, Aucuba, Viburnum tinus, camellia and rosemary, when carried 
after their freezing into a temperature of + 12°, were immediately dis- 
colored; but, having first been submitted to a cold of 18° to 28° C. 
below zero, and then entirely plunged in water of 12° above, they were 
preserved perfectly green for twenty-four hours; if, however, any part 
of these leaves emerged from the water, they turned completely black. 
This remarkable action of the water, independent of its temperature, 
obliges us to seek another explanation of the cause of this phenomenon. 
Here is Hoffmann’s theory : 
The freezing disengaging the air dissolved in the water, a given vol- 
ume of the liquid containing air in dissolution will occupy less space 
when this gas has escaped; moreover, the water, dilated by freezing, 
having ten volumes of liquid, will give eleven volumes of ice.* For 
*Galileo had concluded that the ice which floats upon the water had become dilated 
by freezing. The Florentine Academicians were willing to verify this assertion by 
varied and conclusive experiments ; they certified that the volumes of liquid and solid 
water were to each other as 8 to 9, a relation but little different trom that of +9, which 
pn age. bean found to exist.—Comptes Rendus de Académie de Paris. 1870, vol. 
x, Dp. : 
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