18 The Principles of Fruit-growing. 
350 grams of moisture.” These calculations, there- 
fore, may explain some of the injuries which follow 
very dry winters. 
Since evaporation takes place through the bark 
of winter twigs, it is reasonable to suppose that the 
tenderness of some trees in dry winter climates (as 
in our plains regions) may be due to such an ana- 
tomical structure of the bark as does not resist evap- 
oration, and that, on the other hand, hardiness may 
sometimes be a matter of thickness or denseness of 
bark. Studies in this direction have been made at 
Cornell, and they indicate that this supposition may 
be well founded in certain cases, but the investi- 
gations are not yet sufficiently extended to allow 
of any definite statements. 
The soil determinant.—There are apaeial adaptations 
of fruits to soils. Pomologists are well aware of 
this fact as a general truth, but very little close 
attention has been given, in this country, to the 
minor appleations of it. To be explicit, it is well 
understood that pears flourish best on clay soils and 
peaches best on sandy soils, but there are, no doubt, 
distinct preferences amongst the varieties of pears 
and peaches themselves. It is possible, in fact, that 
each distinct family or type of varieties of any 
species has preferences of land and location, and it 
will be the business of coming generations to de- 
termine what these peculiarities are. With the in- 
creasing refinements and competitions of the future, 
the special and local problems must receive more and 
more attention. If these positions are well taken, it 
