On Changes of Temperature in Plants. 141 



bruary ; that of the tree was higher in March, April, and May, 

 and ao-ain the temperature of the air was higher during the other 

 months of the year. At the beginning of January, the tempe- 

 rature of the tree was higher by 10° 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 4", and even 8° 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 tempera- 

 ture. 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 suc- 

 cessive winters have shewn that the thermometer, in the interior 

 of trees, may descend below zero, without the vegetation suffer- 

 ing. It even descended so low as + 5° Fah., and -f- 1^ Fab. in 

 some young trees. On the 26th January 1828, the thermometer 

 indicated +1^ Fah. ; the day after, it suddenly rose to -1-34^ F. ; 

 the change was not so sudden in the tree, which, the second day, 

 was still below 32° Fah. 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 offered 

 to cutting instruments. In the six trees that were cut, the wood 

 was frozen to the following mean depths : — JEsculus Hippocas- 

 tanum, 8.2 lines ; Pinus Abies, \%6\\ne?,; Acer Pseudo-plata- 

 ni^*, 15.2 lines ; Fraxinus excelsior, \Q.S\\i\e<i; Corylus Avel- 

 lana, 16.9 lines; Salixjragilis, 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 pene- 

 trated into the trees partly in direct proportion to the quantity 

 of water which their wood contained. But much more cer- 

 tain 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, 8 per cent, more of aqueous parts than at the end of Ja- 

 nuary. Water being a better conductor of heat than dry wood, 

 the deleteriofis action of cold upon trees will easily be accounted 



