152 SCIENCE PROGRESS 



describes the " Lignous Body" as forming a "slender Wyer or 

 Nerve," pithless in the smaller roots, but containing a pith in 

 the thicker parts. " The Parenchyma of the Barque, is much the 

 same thing, as to its conformation, which the Froth of Beer or 

 Eggs is, as a fluid, or a piece of fine Manchet, as a fixed Body." 

 The vessels, he finds, are not twisted together or branched, but 

 run straight and parallel side by side. The spiral thickening in 

 the vessels he describes as consisting of " Two or More round 

 and true Fibres, although standing collaterally together, yet 

 perfectly distinct. Neither are these Single Fibres themselves 

 flat, like a Zone ; but of a round forme, like a most fine Thred" 

 Grew observed the radial arrangement of the wood in the root, 

 and propounds a rather mysterious theory to account for it. 

 " 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." He distinguishes between 

 the original skin of the root and the corky covering of old roots, 

 and appears to have had a fairly clear idea of the mechanism of 

 contractile roots. "The String-Roots, . . . which descending 

 themselves directly into the Ground, like so many Ropes, lug the 

 Trunk after them." 



Nehemiah Grew clearly understood the main anatomical 

 distinction between the stem and the root, for he explains that 

 the central position of the ligneous body in the root makes it 

 pliable to an oblique motion, whereas its circumferential position 

 in the stem strengthens it in its upright growth. He also 

 grasped the difference between the origin of stem and root 

 branches. " In the Growth of a Bud, and of-a Trunk-Root, there 

 is this observable difference ; That the former, carries along with 

 it, some portion of every Part in the Trunk or Stalk ; whereof it 

 is a Compendium. The latter, always shoots forth, by making 

 a Rupture in the Barque, which it leaves behind, and proceeds 

 only from the inner part of the Stalk." 



In the case of the stem we find that he recognised the com- 

 pound nature of each vascular bundle ( " fibre " ). Each, he says, 

 is " sometimes perforated by 30, 50, 100, or hundreds of Pores. 

 Or what I think is the truest notion of them, That each Fibre, 

 though it seem to the bare eye to be but one, yet is, indeed, a 

 great number of Fibres together; and every Pore, being not 

 meerly a space betwixt the several parts of the Wood, but the 



