Prof. J. Le Conte on the Freezing of Vegetables. 89 
this may be regarded as a vera causa, but its effect, so far as the 
prevention of freezing is concerned, must be considered absolute- 
ly infinitesimal. ; 
2. That the freezing point of the juices of plants is but slightly 
pressed below that of water, by the admixture of gum, muci- 
lage, and other products of vegetation which impart viscidity to 
them, has been demonstrated by direct experiment. Hunter 
found the freezing point of vegetable juices when squeezed out 
of @ green plant, to vary from 29° to 32° Fahr. In several ex- 
periments on the freshly expressed juice of the strawberry, I 
nd the freezing point to vary from 28° to 30° Fahr. ; and, in 
every case, the temperature after congelation was 30° Fahr. It 
18 extremely probable, nay, almost certain, that the freezing point 
may vary with the degree of inspissation of the sap, and may, 
Consequently, be different for different plants, and at different sea- 
Sons of the year in the same plant; and, moreover, that it may, 
on this account, be somewhat lower in winter than in spring or 
simmer. It is also probable, that the admixture of certain pecul- 
laf Organic products may lower the freezing point of the sap of ‘ 
Particular plants. Thus it is well known to chemists, that the 
Point of congelation of good oil of turpentine is as low as 14° 
Fahe. ; and, perhaps, the presence of this proximate principle, may 
tend to prevent the sap of the Coniferze from freezing in moderate 
degrees of cold. In the present state of our knowledge, it is im- 
Possible for us to assign a definite quantitative value to the influence 
of viscosity in lowering the freezing point of the juices of vege- 
tables; but it is certain that it cannot amount to many degrees of 
temperature.* It must have some influence, and must, therefore, 
be looked upon as a vera causa acting ‘in the right direction ; but 
- Frof. Henslow seems to think that, “the chief protection 
against the sap freezing in the trunks of trees, is the circumstance 
of its being contained in extremely minute vesicles and capillary 
Yessels ; for it has been shown that water will resist a tempera- 
s The fact i ; i i above 
tok tet that the speci avity of the sap of plants is but sli htly aboy 
on Water, affords hse cid pate Bask that the freezing point can a 
the .; for experiments on the admixture of salts with water show, ¢ 
i i the increase of density. 
ground, had a specific gravity of 1004; at seven feet above the 
oe and at beadve tock 1012, (Vide Phil. Trans. for 1805, 
cit. ante, p. 173. a 
Szooxn Seams, Vol. XIII, No. 37,—Jan,, 1852. oe 
