animal kingdom, helped him to take a broad view. "In the Woody Parts of Plants, which are their Bones; the Principles are so compounded, as to make them Flexible without Joynts, and also Elastick. That so their Roots may yield to Stones, and their Trunks to the Wind, or other force, with a power of Restitution. Whereas the Bones of Animals, being joynted, are made Inflexible."
In plants, as in animals, Grew looked for "vessels," and discovered by means of a simple experiment that continuous tubes, worthy of being called by this name, existed in the outer parts of the root, whereas the pith consisted of closed chambers. He cut a fresh root transversely, and then gently pressed the side of it with his finger nail. He was able to detect the vessels with the naked eye, and he observed that where they occurred, sap oozed out under pressure, but was sucked in again when the pressure was removed. The pressure also expressed a certain amount of sap from the pith, where vessels were absent, but here the sap was not sucked in again when the root was no longer squeezed, shewing that the liquid had only been forced out by the wounding of the cells. Had they been open tubes like the vessels, the release of the pressure would have caused the sap to disappear. Grew recognised that the vascular tissue of the root is centrally placed, whereas in the stem it is circumferential, and he points out that this difference is connected with the diverse mechanical needs of the two organs. It should also be noted that he discovered that concentration of the vascular system is characteristic of climbing plants, the wood, in his own words, standing "more close and round together in or near the Center, thereby making a round, and slender Trunk. To the end, it may be more tractable, to the power of the external Motor, what ever that may be: and also more secure from breaking by its winding Motion." He observed the radial arrangement of the xylem in the root, and offered an explanation of it, which is however scarcely free from obscurity. "Some of the more Æthereal and Subtile parts of the Aer, as they stream through the Root, it should seem, by a certain Magnetisme, do gradually dispose the Aer-Vessels, where there are any store of them, into Rays." Amongst other details of root anatomy, Grew discovered that
