10 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



minor modifications, this conception has proved of outstanding success 

 in all of the protein types which Astbury and many other workers have 

 investigated since those early days. Naturally, first attention was paid 

 to the structural proteins like keratin which lend themselves more 

 readily to investigation by X-ray methods. Extension to the so-called 

 globular proteins, which resemble much more closely protoplasm itself, 

 led at first to some confusion, since in these proteins the molecules are, 

 as the name implies, globular and not fibrillar, in shape. It seems now, 

 however, widely agreed that these globular bodies consist nevertheless 

 of protein chains, but closely folded in some specific way. As for proto- 

 plasm itself, it clearly exhibits properties such as streaming, which 

 would harmonize better with the properties of a globular protein, and 

 others such as tensile strength which would seem in better agreement 

 with the properties of the fibrillar proteins. As Frey-Wyssling has 

 pointed out, protoplasm itself may lie half-way between these two ex- 

 tremes and may therefore consist of a loose network of folded poly- 

 peptide chains, in which the features of the whole structure depend 

 therefore as much on the state of folding as upon the constitution of the 

 individual proteins. 



With this vague conception we may well leave the history of these 

 substances and discuss any further points more fully later as and when 

 they are required. 



