56 NEHEMIAH GREW 



all the tissues outside the central cylinder sometimes peel off 

 when the root becomes old, or as he says, " the whole body 

 of the Perpendicular Roots, except the woody Fibre in the 

 Centre, becomes the second skin." Turning to stem structure, 

 we find that he understood the difference in origin between stem 

 buds and adventitious roots. The stem bud, he writes, " carries 

 along with it, some portion of every Part in the Trunk or Stalk \ 

 whereof it is a Compejiditmt." The adventitious root, on the 

 other hand, " always shoots forth, by making a Rupture in the 

 Barque, which it leaves behind, and proceeds only from the 

 inner part of the Stalk!' He describes the vascular bundles 

 of the stem as "fibres" perforated by numerous "pores." It 

 would be a mistake, however, to suppose that he had no under- 

 standing of their structure, at least as regards the xylem, for 

 he goes on to say 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 Concave of a Fiber." 

 He noticed the medullary rays, for which he uses the expressive 

 term " Insertions." " These Insertions," he says, " are likewise 

 very conspicuous in Sawing of Trees length-ways into Boards, 

 and those plain'd, and wrought into Leaves for Tables, Wainscot, 

 Trenchers, and the like. In all which,... there are many parts 

 which have a greater smoothness than the rest ; and are so 

 many inserted Pieces of the Cortical Body ; which being by those 

 of the Lignoiis, frequently intercepted, seem to be discontinuous, 

 although in the Tnink they are really extended, in continued 

 Plates, throughout its Breadth." 



Nehemiah Grew was interested in the process of secondary 

 thickening, but he only arrived at a dim notion of how it took 

 place. He grasped, however, the important point that in a tree 

 trunk the meristematic zone lies near the surface, " the young 

 Vessels and Parenchymous Parts " being formed annually " be- 

 twixt the Wood and Barque." He describes how, " every year, 

 the Barque of a Tree is divided into Two Parts, and distributed 

 two contrary ws.ys. The outer Part falleth off towards the Skin; 

 and at length becomes the Skin it self... The inmost portion 

 of the Barque, is annually distributed and added to the Wood; 



