Trunks of Apple Trees. 185 



If the south side of the trunk is well shielded from the sun, splitting may 

 occur, and then on any side ; but the injury would not be so liable to happen. 

 The condition of the heart of the tree must be an iniijortant item in the ef- 

 fect, but the last season's growth, whether vigorous or not, makes little dif- 

 ference. 



Passing now to the much more serious injury— the separation of bark and 

 wood — we may say that neither the swelling of the interior nor the shrink- 

 ing of the exterior layers of tissues can be accredited with the disastrous re- 

 sults, for these crowd the parts together instead of forcing them asunder in 

 a radial direction. Neither is it in any way the undue shrinking of the in- 

 terior and extension of the outer portions, because no such thing occurs. 

 The heart of a tree always freezes first. No change of temperature is sudden 

 enough in the open air to cause the bark and younger wood to freeze before 

 the pure water of the heart wood congeals, popular opinion to the contrary 

 notwithstanding. The very heart of a healthy tree has more water in it, 

 susceptible of freezing, than has the sap wood and bark, and, if vitality counts 

 for anything, its influence retards the freezing of the outer rather than the 

 inner parts of a tree. During the present winter an excellent opportunity 

 has been offered for observations on this point. When the thermometer first 

 reached zero in December, I examined the twigs of many kinds of trees with- 

 out finding any of them stiffened with ice, except the very immature water 

 sprouts of apple trees and the tall growths of the tender catalpa. The same 

 was true at — 6°. At — 12° the pith of some last season's growths was hard and 

 rigid, and ice was readily seen with 3 hand magnifier. This was observed in 

 apparently fairly ripened twigs of pear — Bartlett and an unknown variety — 

 of some apple trees, of several raspberries, including Turner and Mammoth 

 Cluster, of some shoots of Concord grape (not of those best ripened), of hybrid 

 perpetual roses, etc. On the other hand, the wood and the bark of all these, 

 except water shoots, were still flexible and without ice, while the twigs of 

 most trees, as a whole, were unaffected by ice. At — 28°, in a considerable 

 number of instances, the twigs and the separated wood snapped like icicles, 

 and were found, more or less, crowded with ice crystals ; yet in a greater 

 number of cases the living parts were still flexible and tough. In very few 

 species was the living mature bark, during the coldest period, found frozen — 

 never in ripened Si\)\A& limbs — and these are accounted somewhat tender 

 kinds, such as tulip poplar, the manolias, various roses, peaches, raspberries, 

 etc. The May cherry twigs have at no time during the winter been brittle 

 by freezing. 



It is, however, essentially certain that the bark of apple trees has been 

 forced off by frost, the formation of ice in or near the cambium layer. It 

 has not been my fortune to actually observe the phenomenon for the pur- 

 pose of verifying the conclusions otherwise reached; it is difficult to find the 

 affected trees or areas until long after the injury is done and the operating 

 cause removed, and no artificial experiments have been tried. I venture 

 however, the assertion, that it is the growth of the forest of ice crystals from 

 13 



