126 AGRICULTURAL REPORT. 
must be deprived of their principle of vegetation before they can be 
frozen.” Again he says: “ But the question is this: Is every tree dead 
that is frozen? I can only say, that in all the experiments I ever made 
upon trees and shrubs, whether in the growing or active state, or in the 
passive, that whole or part which was frozen was dead when thawed.” * 
_ Notwithstanding that great authority, it is well. known to practical 
horticulturists that the pernicious consequences of severe cold on grow- 
ing plants may to some extent be obviated by careful and gradual thaw- 
ing; in such cases the freezing is incomplete, and does not involve all 
of the structures of the plant. 
Haiiyt thought at first that frost acts mechanically upon the tissues 
of plants, by expanding the fluids they contain, and thus bursting the 
celis or vessels in which they are inclosed. References might be multi- 
plied to show how universal this opinion has been, and still is, among, 
some of the best physiologists. Although most of them reject the idea 
of Hunter, they appear to be of the opinion that after complete conge- 
lation the plant necessarily dies. 
H. R. Geepperti was the first to prove, in 1829, that the changes which 
plants undergo, when they are killed by cold, do not consist of the burst- 
ing of their cells or vessels, but solely of an extinction of their vitality, 
which is followed by alterations in the chemical composition of their 
. juices. In the winter of the same year Charles Morren made some ex- 
periments on the action of cold and frost upon plants, and arrived at the 
same conclusions deduced by Geppert, although his theory differs in 
some respects from that of the latter author. The following are his 
deductions, from a more recent publication :§ 
1. That no organ whateveréis torn by the action of frost, except in 
very rare cases, when the vesicles of cellular tissue give way to the ae- 
tion caused by the expansion of the liquid. 
2. That the organs contained in the cellules, or the vesicles, undergo 
no alteration, unless perhaps in the case of the femla, which in some 
circumstances is converted into sugar, no doubt in consequence of the 
action of some acid formed by the decomposition of the organic parts. 
3. That the biforines do not cease the ejaculation of their raphides 
after freezing, and therefore it is probable that this movement is not due 
to a vital contractibility. 
4, That the,action of frost operates separately upon each individual 
elementary organ, so that a frozen plant contains as many icicles as there 
are cavities containing fluid, the dilatation thus produced not being suf- 
ficient to burst the sides of the cavities. 
5. That such dilatation is principally owing to the separation of the 
air contained in the water. 
6. That it is to be supposed that since the sap, the latex, the liquid of 
the cells, and all the fluids which are found in plants are not composed 
of pure water, vegetation by this condition resists freezing, within cer- 
tain limits; as the experiments of Blagden have praven, the matters 
which taint the purity of the water allow the liquid to attain a degree 
of cold, while in their absence it would be frozen. 
7. That the disengagement of air from water, during the act of con- 
* Philosophical Transactions, 1775, vol. Ixv, pp. 446-458, 1778; vol. lxvili, pp. 7-49. 
tTraité elémentaire de Physique. Paris, 1806, vol. i, p. 209. 
tOkens Iris, Breslau, 1830, p. 497, briefly abstracted; trans. in Edinburgh Jour- 
nal of Natural and Geological Science, 183i, p. 180. Ueber Wirmemtwickelung in 
der lebenden Pflanzen. Breslau, 1830. Wien, 1832. 
§ Bijdragen tot de natuurkundige Wetenschappen, 1830, vol. v, pp. 55-77; Bulletin 
de Académie des Science de Bruxelles, 1238, vol. v, pp. 93-111. 
