THE VASCULAR SYSTEM 55 



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 dis- 

 covered 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 wound- 

 ing 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 dis- 

 covered 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 ^Ethereal 

 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 



