TTHE LIBRARV. V9 



action of the temperature of the air, and to the occasional 

 sunshine, so that the degree to which it is heated or 

 cooled down, depends, when the conditions are the same, 

 on the degree and duration of the sunshine or the shade. 

 And in this respect the trees which are in a clump are 

 differently affected from those which are isolated. The 

 rapidity with which, other things being equal, the mass of 

 a tree becomes warmed, depends on the surface and thick- 

 ness of the bark, and on the conducting power of the 

 roots and the wood in regard to heat. Wood in general 

 is a bad conductor of heat, but all species are not alike in 

 this respect. The influence of the specific heat of the 

 bark and wood, as well as the chemico-physiological func- 

 tions of the tree, however, we shall not here take into 

 account. 



' Differences in the size and diameter of the .tree pro- 

 duce differences in its temperature. The daily oscillations 

 and the maximum temperature of the trunk are so much 

 the greater as the diameter of the trunk is less or as the 

 point of examination is nearer to the surface. The ther- 

 mometer shows a higher temperature in the branches than 

 in the trunk ; and so much is it so as to show the tem- 

 perature indicated by thermometers introduced into the 

 trunk branch and branchlet to be in inverse proportion to 

 the respective diameters of these. 



' From this, then, it is deduced that the internal tem- 

 perature of a tree takes a character related to and is 

 produced by a great many circumstances having a reaction 

 upon one another. It is therefore necessary, in order to 

 similar observations being comparable together, that they 

 should be made under identical conditions, and exact 

 accordance in the location of the thermometers, in the 

 height and depth of their position, the diameter of the 

 trunk at the point at which the temperature is observed, 

 and finally in the measure of sunshine or shade. 



' All of these particulars serve as a basis to determine 

 at three different heights the influence which the cooling 

 effect of the roots and the crown of the tree exercises on 



