SOME SEASONAL CHANGES IN THE TRACHEAL SAP OF PEAR AND APRICOT TREES

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Abstract
Preliminary data are reported, including determinations of buffer value, reaction, content of electrolytes, individual inorganic constituents, free reducing substances, sucrose, nitrogenous compounds, and total solids in tracheal sap of pear or apricot branches at various times during the year. The radial distribution in tracheal sap of acidity, total electrolytes, and free reducing substances before and after inversion is also shown for pear branches during the early spring. The buffer value of tracheal sap at the middle of spring is about 1/25 that of expressed sap from the same tissues. Tracheal and expressed sap reached maximum acidity in early spring, then fell gradually to minimum acidity in winter. The change from minimum to maximum acidity in early spring was very rapid and coincided with the resumption of growth. Total electrolyte concentration and increased acidity of the tracheal sap ran parallel. Individual inorganic constituents in the tracheal sap showed a large increase in concentration from early winter to early spring. Phosphate in the tracheal sap showed a very large increase between late winter and early spring. It is suggested that this increase is due in large part to phosphate set free in the hydrolysis of starch. Free reducing substances and sucrose showed a high concentration in late winter and early spring, a rapid decrease in late spring, an indeterminable low amount during summer, and a gradual rise during fall and winter. The total solids, determined refractometrically, rose during the winter months and declined during the spring, and then remained relatively uniform during the remainder of the yr. The free reducing substances and sucrose were found to be limited to the outer annual ring in 3-yr.-old pear branches during late winter and spring. Total electrolytes were about twice as concentrated in the outer annual ring as in the inner rings. The sap from the outer annual ring was more acid than that from the inner rings.

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