It has been shown that cerebral oxygen consumption and blood flow are normal and cerebral vascular resistance is increased in patients with essential hypertension (1). Clinicians have questioned the advisability of lowering arterial pressures in hypertensive patients because of the possible untoward effects consequent to decreased cerebral blood flow (2, 3). We have studied the effect of hypotension, induced by various means, on the oxygen consumption and blood flow of the brain.During the hypotension obtained one hour after the injection of dihydroergocornine (4), protoveratrine (5), hexamethonium (6), and 1-hydrazinophthalazine (7), cerebral blood flow and oxygen uptake were unchanged. Cerebral oxygen uptake was unchanged and cerebral vascular resistance was decreased during the hypotension induced by differential spinal sympathetic block (8). After thoracolumbar sympathectomy, cerebral blood flow and oxygen uptake remained constant and the cerebral vascular resistance was reduced toward normal values three weeks to six months after operation (9). Thus, in most of these instances, cerebral blood flow was not reduced and cerebral oxygen consumption remained unchanged when the arterial pressure was lowered either by the drugs tested or by surgical sympathectomy. These hemodynamic observations suggested that the cerebral circulation remains adequate when the blood pressure is lowered. The increased cerebral vascular resistance in hypertension apparently can be reduced by certain measures without reducing cerebral oxygen consumption and cerebral blood flow. ' This investigation is being supported, in part, by research grants from the National Heart Institute, U. S. Public Health Service (H-361)

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2C values for angiosperms vary over 2500-fold and a positive correlation exists between C-value and latitude in herbaceous plants. Woody plants differ from herbaceous plants in chromosome size and C-value. In addition, tropical hardwoods have smaller chromosomes than other tropical plants and do not share the correlation of minimum generation time with genome size seen in herbaceous plants. Theobroma cacao is a tropical hardwood cultivated for its beans, which are used to make chocolate and cocoa butter. Its cytology is typical of the pantropical and subtropical family Sterculiaceae. Its small chromosomes, single secondary constriction, and lack of C-banding suggest a small genome. The genome size of T. cacao, measured by reassociation kinetics, is 2.01 x 10(8), which is small compared to both temperate and tropical plants previously studied. We also provide data on the melting point, base composition, and relative extent of methylation (at sites most commonly methylated in higher plants), of T. cacao DNA.