PHYSIOLOGY. OAS 
gree of heat, is a question which remains to be an- 
swered. We find that trees or shrubs, in cold cli- 
mates, if they grow wild, can bear the greatest cold 
without harm. As soon as the-warmth of the s spring 
commences, their buds are evolved, and they shew 
no bad effects from the cold whatsoever, though 
their stem and branches be full of moisture. If in 
a strong frost we put vessels with water alongside 
of such a tree, «we will find that the water is frozen, 
but that the tree retains its sap unfrozen, and is not 
in the least hurt. ‘The contrary takes place in plants 
of warmer and hot regions. Their sap congeals at 
the least degree of cold, and the plants decay. ‘Thus 
there is evidently a remarkable difference between 
the plants of cold and those of hot ¢limates. As 
long as plants live and possess sufficient vital power, 
to resist cold, their sap will not congeal with cold. 
But when in spring cold nights come on, after the 
buds have burst, the new shoots perish through frost. 
We observe, likewise, that dead or sick branches 
are more exposed to be frost-bitten than living 
and sound ones, and that branches, by their sap 
being congealed, are killed.’ The birch and some 
other plants, it is well known, often have their roots 
covered with ice, without suffering the least injury. 
In the northern hemisphere of our globe are many 
and extensive tracts of pine trees, which resist with 
their evergreen branches the most violent winter 
cold. ‘Those observstions clearly prove, that each 
plant possesses a peculiar degree of wa armth accord- 
ing to its species, which defends it against the incle- 
mency of the weather. 
Onan ny But 
