Various tissues in flower buds of Pyrus calleryana Decne. differ in their metabolic activity. Brown outer scales utilized more exogenously supplied glucose, particularly through the pentose phosphate pathway, than did the central axes and the green inner scales. They also contained more endogenous reducing sugars, and glucose leaked out more readily from the brown scales than from the other tissues. In contrast, respiration of the central axes was nine times as great as that of the brown scales, and two to four times as much glucose was metabolized through glycolysis. Membranes of the central axes were less permeable to glucose. Because the brown scales are 75% of the dry weight of the bud, they domiinate its pattern of glucose metabolism.The resting flower bud of a tree is a complex organ composed of at least three different tissues: the brown outer scales; the green inner scales; and the central axis. In studying metabolism of buds, most investigators have used the entire structure and found that the metabolism resembled that of old rather than of young tissues. Thom's work (17), which included a comparison of bud parts, is a notable exception.In developing a procedure for extracting RNA from pear buds, we found that unknown substances in the brown scales interfered with the extraction of nucleic acids from the central (3,5,9,12,16,18). Buds also contain a substantial amount of fatty material (6). In the bud cells the deposition of a lipoid layer on the surface of the protoplasm is associated with the separation of the protoplasm from the cell walls (7). As the plants leave the rest period the protoplasm absorbs water and swells (6, 19). Glucose metabolism changes during swelling. The contribution of the pentose-P pathway to respiration decreases and the role of the Embden-Meyerhof-Parnas glycolytic pathway increases during this time (19). The change in water content of buds during swelling indicates that resting buds are relatively dry. Dehydrated tissues have been shown to respire more through the pentose-P pathway (11), and this can be accepted as an explanation for the relatively high pentose-P pathway activity in resting buds. The state of dehydration may mimic the effect of the age of the tissues with respect to their respiratory pattern.Another measure of cell age is the permeability of cell membranes. Increases in permeability of cell membranes with age were observed in apples (4), avocados (15), bananas (2), and bean endocarp (10) and are considered normal for senescing tissues (13). MATERIAS AND METHODSPlant Material. Terminal flower buds from two 7-year-old trees of Pyrus calleryana Decne. were collected between midJanuary and mid-March 1970. The upper portion of both trees had flowered at least four times before the start of the experiment. We cut shoot tips from the tree 5 to 8 feet above ground and brought them into the laboratory. There we excised the terminal buds and stripped away all the bud scales. The outermost two or three scales were discarded and the remaining scales were separa...