143 
ON CHANGES OF TEMPERATURE IN PLANTS. 
In a thesis sustained at the University of Tubingen^ Dr. W. NeufFer has 
presented the results of a number of interesting researches into the changes of 
temperature which plants undergo. In a thesis presented by M. Haider, in 1826, 
on the same subject, the author asserted that trees are in winter at a lower tem- 
perature than the freezing point, and even pass to the state of congelation without 
injury to their life. The winter of 1827 and 1828 being very severe, the necessary 
observations were made at Tubingen for confirming those of M. Haider. The 
temperature of a poplar was observed during the whole of the year 1828, and the 
results of this examination differ little from those obtained in the Botanic Garden 
of Geneva, and published in the first volume of the Bibliotheque Britannique. 
The temperature of the air and that of the tree were about equal in February ; that 
of the tree was higher in March, April, and May ; and again, the temperature of 
the air was higher during the other months of the year. At the beginning of 
January the temperature of the tree was higher by ten degrees than that of the 
external air, which would appear to announce a great disengagement of heat at the 
time when the aqueous juices of trees congeal. When it thawed, the heat of the 
tree was four degrees, and even eight degrees, above that of the air. It is to the 
greater evaporation of trees in summer, that the author attributes the less elevated 
degree of their temperature. The reason of their heat being greater in spring is, 
that they then lose very little by evaporation, and retain the mean temperature 
of the earth, which at that season is a little higher than that of the air. The 
observations made during two successive winters have shown that the thermometer, 
in the interior of trees, may descend below zero, without the vegetation suffering. 
It even descended so low as — r5° Fahr., and — 11° Fahr. in some young trees. On 
the 26th January, 1828, the thermometer indicated + 1J° Fahr.; the day after it 
suddenly rose to + 3410 Fahr. j the change was not so sudden in the tree, which, 
the second day, was still below 32° Fahr. Several trees were cut, and they were 
found frozen in concentric circles to a certain depth. The frozen wood was easily 
known by the greater resistance which it ofi'ered to cutting instruments. In the 
six trees that were cut, the wood was frozen to the following mean depths: — 
Msculus Hippocastanurrij 8.2 lines; Fraxinus excelsior, 12.5 lines; Acer Pseudo- 
platanus, 15.2 lines; Fraxinus excelsior, 16.8 lines; Corylus Avellana, 16.9 lines; 
Salix fragilis, 17.3 lines. The water in a pool near these trees was frozen to the 
depth of 8.8 inches. 
Experiments, made with care, prove that the cold had penetrated into the 
trees, partly in direct proportion to the quantity of water which their wood con- 
tained. But much more certain results were obtained by the examination of the 
concentric layers of different trees, and the result was, that the cold had penetrated 
least into the trees whose layers were closest. 
In spring the cold often causes trees to perish, without their having been injured 
by it in winter. On this subject the author apprises us that nearly all trees contain 
at the beginning of April eight per cent, more of aqueous parts than at the end of 
