CARBOHYDRATE CHANGES WITHIN THE NEEDLES OF PINUS PONDEROSA AND PSEUDOTSUGA TAXIFOLIA

The ability of most coniferous trees and of certain other plants to retain their foliage over several seasons has attracted considerable attention among botantists. This interest is especially keen concerning those plants subjected to extremely cold winters, and which, with rare exceptions, must possess the property of cold resistance, at least during the actual duration of the periods of subzero temperatures. It has long been known, even by the layman, that such coniferous needles are not, in general, resistant to cold during the warmer months of the year. Consistent studies of the seasonal variations in the physiology of a plant, as well as parallel studies of the variations in the habitat-factors, are necessary to reach an understanding of that species' ability to survive under the environmental conditions representing a given habitat. It has long been recognized that the polysaccharides in leaves, under certain climatic conditions, are converted into the simpler saccharides, and vice versa, by what appears to be the shifting of an equilibrium by means of enzymatic activities. These seasonal variations in the amount and chemical nature of food reserves in the cells of evergreen leaves are in themselves of physiological significance. Although many workers have contributed much important data on this subject, including carbohydrate, osmotic pressure, and pH measurements, our actual information is still fragmentary. This problem was undertaken to ascertain the quantitative fluctuations of various classes of carbohydrates in Pinus ponderosa and Pseudotsuga taxifolia needles throughout the more or less dormant season, and to determine a possible relationship between the saccharide fluctuations and the temperature changes.