182 Mississippi Valley HortiGultural Society. 



structure only, and at a much lower temperature. If a limb is cut from a 

 living tree, harily in our climate when the temperature is at zero, and has 

 not immcdiatel}' preceding been much lower, neither the bark nor the Avood 

 will ordinarily be found frozen. A separated sliver is still flexible, and no 

 ice crystals can be seen with the microscope ; but a drop of water applied to 

 the surface, even soon after the stick has been taken into a warm room, in- 

 stantly congeals as it does on similarly cold iron. Yet in this green stick 

 there is forty per cent, of its weight water, existing there unfrozen at zero, 

 Fahr., not as a liquid, but caj^able of being evaporated from the tissues at 

 the temperature of boiling water. 



When this water does freeze in some of our trees at about — 12° to — 20° 

 Fahr., a minute thin plate is first formed on the surface of the structure, or 

 rather multitudes of such thin plates of regular shapes, are thus formed near 

 together. With a little further decrease of temperature, other water mole- 

 cules are wrested from their attractions in the woody structure and arrange 

 themselves beneath those first formed, and in so doing push the latter out- 

 ward. This escape of some of the water from among the cellulose mole- 

 cules causes the latter to approach nearer each oiher, and at the same time 

 to hold with stronger power the remaining water molecules which only join 

 their fellows in the crystal at a still lower temperature. As, however, the 

 cold increases, the crystal pushes out, not gaining in diameter, but increas- 

 ing in length by constant additions to its base, just as we may conceive of the 

 erection of a chimney by successively placing bricks under those already 

 laid and pushing upward the whole structure. The final length of the crys- 

 tal depends upon the amount of water and the degree of cold. Sometimes 

 frozen succulent plants may be seen thickly coated with a crust of such crys- 

 tals a fourth of an inch or more long, but so slender that a magnifier is needed 

 to identify individual ones, the whole presenting to the naked eye a some- 

 what velvety appearance. Similar crusts are formed in the interior of the 

 tissues on the surfaces of certain kinds of cells and pushing into cavities 

 caused by the shrinking of the material. 



We may now consider that we have the chief facts upon which the ex- 

 planation of the two forms of injury to tree trunks by freezing rests. We 

 have compared the splitting of the trunks to the familiar bursting — too fa- 

 miliar — of iron water-pipes and water-pitchers. It is only necessary that a 

 sufficient amount of water in the liquid state exists in the central parts of 

 the tree, and that a sufficient degree of cold be reached, to shrink the woody 

 fiber and congeal the fluid. If the water, though as a liquid in the ducts, 

 cell-cavities and intercellular spaces, contains substances in solution like sugar, 

 earthy salts, etc., freezing will be more or less below 32° Fahr. ; and this is 

 normally the case. If the water exists only in the imbibed state in the cell- 

 walls, a much lower degree than this will be rcquircil to produce crysUdliza- 

 tion, and this is the normal winter state of a hardy and sound tree. It is 

 only in spring-time, or in a spring condition of tilings, that any liquid water 

 ■exists in such trees. On microscopic exaininatiim in winter, no water as 



