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Mobilization of protein nitrogen in the spring was studied in bark of stems of unringed and double stem-ringed apple rootstocks M.7 given different nitrogen treatments.A ready protein hydrolysis occurred; the proteins contributed the greater part of the storage nitrogen exported to tlie growing parts. Protein hydrolysis was little affected by the suppjy of newly absorbed nitrogen. Movement of nitrogen out of the bark between the rings could not be demonstrated. Protein breakdown in the isolated bark sections was slightly reduced.Arginine was the predominant amino acid in the proteins of the trees with a high level of storage nitrogen but was not conspicuous in the low-nitrogen trees. The protein composition changed little during hydrolysis. Only the share of arginine in the Hgh-nitrogen trees dropped appreciably. It is suggested that the high-nitrogen trees possess a special storage protein characterized by a high arginine content.Analysis of the nitrogen fraction of isolated bark sections stowed that the composition of the soluble nitrogen was characterized by a high level of asparagine and especially of arginine» and was qtiite different from the composition of the proteins. The data suggest that the asparagine in particular originated largely from transformation of the various amino acids set free during protein hydrolysis.

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