SEASONAL CHANGES IN TOTAL, SOLUBLE, SOLUBLE-PROTEIN, NON-PROTEIN, AND INSOLUBLE NITROGEN IN CURRENT YEAR'S SHOOTS OF BARTLETT PEAR

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Abstract
Samples, taken from 12 six-yr.-old Bartlett pear trees, were collected at intervals of 1 mo. from Sept. 1927 to Jan. 1929. Samples were separated into bark and wood, dried at 50[degree]C, and ground to hundred mesh; they were extracted with cold water for 2 hrs. to get soluble N. Soluble protein was precipitated by colloidal Fe, heat, and pH adjustment. Results (calculated on dry weight % basis) were: total N, bark 0.8-1.1, wood 0.5-0.7; total water-soluble N, bark 0.18-0.22, wood 0.25-0.35; water-soluble non-protein N, bark 0.1-0.15, wood 0.2-0.3; water-soluble protein N, bark 0.05-0.1, wood 0.04-0.06; insoluble N, bark 0.6-0.9, wood 0.25-0.35. Total N of new growth, especially bark, is high. It decreases as the growth proceeds, but again increases towards the period of cessation of active growth, reaching a max. in winter. It falls again in spring because of the demands of the new buds. Seasonal changes in total N are mainly due to changes in insoluble N in the bark and the soluble N in the wood. Soluble-protein N which forms only a small fraction of the total N both in bark and wood, shows an increase in late summer and autumn, and a fall in later winter and spring.
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