VIEWS ON ANATOMY 95 



his statement. Also he realized that the wood vessels were in 

 some way connected with water : 



"These vessels arise in the substance of the Wood, principally 

 towards the outer edge of each circle. They are very large in 

 the outermost coat ; and smaller in the others : and there are 

 also irregular ranges of them, running thro' the thicknesses of 

 the circles ; besides these principal ones of the outer course. 

 They have solid, and firm, coats ; and they contain in Spring, 

 and at Midsummer, a limpid liquor, like water, but with a slight 

 acidity : at all other seasons of the year they appear empty, 

 their sides only being moistened with the same acid liquor. 

 Those who examined them at such seasons, thought them air 

 vessels ; and in that opinion, formed a construction for them, 

 which Nature does not avow." 



Although Hill recognized the entity of the cell he had, in 

 common with his contemporaries, no clear conception of its real 

 nature. 



In describing the pith of the rose he does not go astray, and 

 he fully appreciated that the seemingly double contour of the 

 cell walls, when seen in some sections, is due to the thickness of 

 the section with consequent overlapping of the cells ; on the 

 other hand he went very wrong in the case of the pith of the 

 walnut, the cavities of which he supposed to be cells like those 

 of the rose, only very much larger and uniseriate as the following 

 quotation shews : 



" The Pith of the Walnut consists only of one range of these 

 bladders [' Blebs ' or cells], smaller at the edges, largest in the 

 middle, and laid very exactly one upon the other." 



When he considers the structure of more or less square or 

 oblong cells his ideas are very wrong. In such cases he thought 

 that the transverse walls were spaces, and the longitudinal 

 walls vessels ; curiously enough Hedwig made a similar mis- 

 take some years later, possibly he was led astray by Hill's 

 misconception. 



Hill adversely criticized the theory that the pith is an organ 

 of propagation, and substituted the view that the corona i.e. the 

 peri-medullary zone is all important in this connexion, " From 

 it arises the branches, and encrease of the tree." 



