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470 of growth. It found a new supporter in 1680 in the person of Claude Perrault, who does not however appear to have added anything essentially new to Malpighi's conclusive arguments for a returning sap. Nor did his opponent Magnol in his very weak treatise published in 1709 succeed in saying anything that will bear examination against the theory of circulation, which he too ascribed to Malpighi.

Among the phenomena of vegetation in woody plants, there is scarcely one so striking as the outflow of watery sap from wounded vines and from some tree-stems in the spring. This phenomenon, like the outflow of milky juice, gum, resin and the like, could not fail to be regarded with lively interest by those who occupied themselves with vegetable physiology in the 17th century. Even supposing the movements of water in the wood and of the milky and other juices in their passages not to be necessary accompaniments of the nutrition of plants, yet it was natural that the physiologists of the 17th century should see in them striking proofs of that movement of the sap which is connected with nutrition, and should therefore make them a subject of study. It might also seem to them that the problem in question was easy to solve, for it was not till long after that it came to be understood that these movements are in reality one of the most difficult questions of vegetable physiology. We discover the interest taken in these matters from a series of communications in the form of letters from Dr. Tonge, Francis Willoughby, and especially from Dr. Martin Lister, to be found in the Philosophical Transactions for 1670. The phenomenon to which these men chiefly directed their attention was just the one best calculated to