’ AGRICULTURAL METEOROLOGY. 127 
gelation, is the most injurious of all the phenomena attendant upon 
freezing, introducing gaseous matter into organs not intended to elabo- 
rate it, and bringing about the first stages of decomposition in the sap 
and its precipitates, so that with a thaw commences a new chemical 
action destructive to vegetable life. 
8. That the expansion of the cells and aquiferous organs drives a great 
quantity of water into the air cells and air vessels, so that the apparatus 
intended to convey liquid only contains Water and air, while that 
which is naturally’a vehicle for air conveys water. Such an inversion 
of the functions must necessarily be destructive to vegetable life, even 
if death were not produced in frozen plants by the decomposition of their 
juices, the loss of their excitability, and the chemical disturbance of all 
their contents. 
. After some experiments made during the winter of 1550~51, Professor 
John Le Conte reached the conclusion that the sap of trees and shrubs 
which are uninjured by extreme cold does become frozen without the 
slightest damage to them; the reverse opinion being generally prevalent 
among the most eminent physiologists. Subjoined are his conclusions: 
1. That the sap of certain plants can be readily frozen by the appli- 
cation of a comparatively moderate degree of cold. 
- 2. That the congelation of the juices of vegetables does not, as many 
physiologists imagine, necessarily and inevitably result in the death of 
the whole plant, or of the part in which it takes place; but that, on the 
contrary, frequently no injurious consequences follow. 
Professor Le Conte also thinks that “the hypothesis of the laceration 
of the vegetable tissues is totally untenable, for it seldom, if ever, takes 
place, even when the most succulent plants are frozen and killed by cold. 
During the process of congelation each cell of the tissue becomes indi- 
vidually larger by the increase of volume which attends the solidifica- 
tion of the contained fluid; but there is no bursting, because the mem- 
brane is extensible, and when thawed it recovers its first state by its 
elasticity. Although in some instances Professor John Lindley has 
foundsthe tissue of the succulent parts of plants lacerated, as if by the 
dilatation of the fluid they had contained, yet this result was by no 
means an invariable concomitant of freezing, and it is not essentially 
connected with the destruction of vegetable life.”* 
Aug. Pyr De Candolle explains how plants endure the .action of ex- 
cessive cold, by the following facts, which may prevent their juices from 
freezing: 1. A certain amount of proper heat, generated by physiologi- 
cal actions. 2. The viscosity of the juices lowering the freezing point. 
3. The distribution of the sap through minute vesicles and capillary 
vessels depressing the point of congeiation still further. 4. Theavarmth 
of the ground from which the sap is pumped up. 5. The low conduct- 
ing power of consecutive layers of bark, with entangled air included in 
their meshes, and of the wood itself, where the power is less transversely 
than longitudinally. t 
Professor Lindley concludes that the fatal effect of frost upon plants 
is a more complicated action than has been supposed, of which the fol- 
lowing are the more important phenomena: 1. A distention of the cel- 
lular succulent parts, often attended by laceration, and always by a 
destruction of their excitability. 2. An expulsion of air from the erifer- 
ous passages and cells. 3. An introduction of air, either expelled from 
the air passages or discharged from the water during the act of freezing, 
into parts intended exclusively to contain fluid. 4. A chemical decom- 
*American Journal of Science, 1852, vol. xiii, p. 204. 
t Physiologie Végétale. Paris, 1832, vol. iii, p. 1101. 
