4 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



types he saw and figured for the first time (he was the first to use the 

 term parenchyma for instance) he gave early attention to the walls of 

 vessels. On mechanical treatment of these he found them to unwind 

 like flat ribbons and of these ribbons he says (1682) (Plate I): 



... the Vessles, oftentimes, unroave in the form of a Plate. As if we 

 should imagine a piece of fine narrow Ribband, to be woutf d spirally, 

 and Edg to Edg, round about a Stick; and so, the Stick being drawn out, 

 the Ribband to be left in the Figure of a Tube, answerable to an Aer- 

 Vessel. For that which, upon the unroaving of the Vessel, seems to be a 

 Plate, or one single Piece, is, as it were, a Natural Ribband, consistmg 

 of several pieces, that is, a certain number of Threds or Round Fibres, 

 standing parallel, as the Threds do in an Artificial Ribband. And as in 

 a Ribband, so here, the Fibres which make the Warp, and which are 

 Spirally continu'd; although they run parallel, yet are not coalescent; 

 but contained together, by other Transverse Fibres in the place of a 

 Woof. 



He became convinced that all other cell types follow this structure, and 

 concluded in general that the threads in parenchyma cell walls lie 

 horizontally while those of fibres lie vertically. Let us notice particularly 

 the fineness to which he considered these threads could be split. 



So in the Pith of a Bulrush of the Common Thistle, and some other 

 Plants; not only the threds of which the Bladders; but also the single 

 Fibres, of which the Threds are composed; may sometimes with the help 

 of a good Glass, be distinctly seen. Yet one of these Fibres, may reason- 

 ably be computed to be a Thousand times smaller than an Horse-Hair. 



This latter estimate can hardly be accepted since the fibres would then 

 have been ofthe order of 0-1 or 0-2/i in diameter. It does seem reasonable 

 to assume, however, that Grew had seen threads grading in fineness 

 down to the limits observable. Some two hundred years later Sachs, 

 the foremost plant physiologist of his time, was to ridicule these sug- 

 gestions made by Grew; yet it is very instructive to examine his figures, 

 of which one is presented in Plate I, in the light of modern obser- 

 vations with an electron microscope (Frontispiece). It is always easy, of 

 course, to read modern ideas into older and vaguer writings, but here 

 Grew expresses himself so unequivocally that one can hardly avoid the 

 conclusion that this interpretation, in terms of what we would now call 

 fibrils, was inspired vision. We are to see the idea of fibrillar structure 

 turning up again and again in the years that followed, both in the wall 

 and in the protoplasm, and equally often being ridiculed. Grew was 

 undoubtedly an acute observer; among other things, he realized that the 

 walls of parenchyma cells were complete, without perforations, a point 



