COMPOSITION AND GROWTH INITIATION OF DORMANT BARTLETT PEAR SHOOTS AS INFLUENCED BY TEMPERATURE

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Abstract
Dormant Bartlett pear trees were maintained throughout the winter and spring months (1) in cold storage at a constant temp. (2[degree] C.) ; (2) in the greenhouse where the temp. never fell below 16[degree] C.; (3) at the variable intermediate temp. condition outdoors. Those in (2) remained practically dormant throughout the year; those in (1) and (3) became capable of growth; those in (1) which were subjected to a lower temp. than in (3), were first to finish their rest period. At frequent intervals shoots were removed from the trees for analysis to ascertain the changes in certain constituents taking place under each of the temp. conditions. In (1) and (3), both of which resulted in a breaking of the rest period, the following changes in the composition of the shoots were found: An increase in hexose sugar, sucrose, organic acids, and freezing point depression of the expressed sap, while starch markedly decreased. Little change in these constituents occurred in the trees of group (2). No effect of the different temp. conditions was found in the following determinations: non-hexose reducing substances, water-soluble polysaccharides other than starch, arbutin, fats, total N, amide N, and electrical conductivity of expressed sap. The changes reported as the result of exposure to low temp. have not been established as necessary to the initiation of growth; however, growth did not take place in the absence of these changes.