128 AGRICULTURAL REPORT. 
position of the tissue and its contents, especially the chlorophyl. 5. A 
destruction of the vitality of the latex, and a stoppage of the action of 
‘its vessels. 6. An obstruction of the interior of the tubes of paren- 
chyma, or woody fiber, by the distention of their sides. In another 
place Professor Lindley says: 
It has been suggested that the fluids contained in different species of plants 
may themselves act differently in the presence of cold, just as the oil of turpentine 
requires a temperature of 14° to freeze, while oil of bergamot freezes at 23° and olive 
oil at 36°. This may be trne toa limited extent, but it does not explain the phenomena. 
The plant x perishes from frost, for instance, while another, identical with it in nature, 
lives with impunity within two yards of it, both having been exposed to the same 
temperature. The finids of the two will be chemically the same, and yet the results 
are opposite; except it would be in proportion to the quantity of water they contain, 
but not as to the quality of their fluids, that they have the power of resisting cold. 
Some plants are also killed by cold although their cells are perfectly empty, in whieh 
case we need not say that the expansive force of frozen fluid could have nothing to 
operate upon. All the experience that forty years’ acquaintance with such phenomena 
has given us leads to one, and only one, conclusion, which is, that the power of resist- 
ing ae is the consequence of specific vitality, and of nothing else. It may be asked, 
what is this specific vitality? ‘To that we have no reply to give, except that we do 
not know.* 
As stated heretofore, Geeppert had already advanced the idea of the 
extinction of vitality in plants, followed by some chemical decomposi- 
tion of their juices, by the action of frost upon them. At the same 
time Morren had shown the pernicious influence of air in the cells of 
their tissues as being the probable cause of that decomposition. Based 
upon these two conclusions, and on his own experiments, Hoffman has 
given the most satisfactory explanation concerning the action of frost 
upon plants, as shown in the following investigations of that conscien-_ 
tious observer : . 
During the winter of 1855, when the thermometer descended as low 
as 279.7 C., Herman Hoffmann made numerous observations upon the 
influence of frost on vegetation. The most frequent frost did not nota- 
bly change the aspect of the plants which it reached; they grew stiff- 
ened, often almost brittle; frequently they contracted some little, but 
their color sustained no important alteration. It made little difference 
with the tenderer plants whether the frost was 12° or 24° below zero 
for half an hour, or for twenty-four hours or more, providing it was not 
interrupted an instant by an elevation above zero, and that it pene- 
trated into all their organic substances. In other rare cases the frost 
considerably changed the aspect of the plants, which result we may not 
foresee by the consistence of their leaves, their native country, their 
age, &c. The epidermis was detached in plates from the green paren- 
chyma of the leaves without tearing, and presented the appearance of 
blisters raised on the skin by a burn, appearing to be filled only with 
air. The action of frost often changes the normal position of the organs. 
Hoffman saw the scented tulip bent and straightened more than ten 
consecutive times, according as the temperature feli below or rose above 
zero. 
All plants do not support the alternations of freezing and thawing; 
@ very great number are killed by the thaw, and not, as ordinarily 
thought by the frost; such are the tropical plants. The delicacy of a 
plant, and the quantity of juices which it contains do not furnish any 
sure indication of its sensibility to the frost. The delicate crocus, for 
*Transactions of the Horticultural Society, London, new series, vol. p. 308, ab- 
stracted by Professor A. Gray in the American Journal of Sciences, 1840, vol. xxxix, 
pp. 18-28. The Theory of Horticulture, New York, 1859, p. 85. The Magazine of 
Horticulture, 1855, vol. xxi, pp. 391-394. 
