176 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



cellulose diagram but, instead, only two vague rings characteristic of 

 water in bulk. On drying, the water haloes naturally disappeared and at 

 the same time the famihar cellulose diagram was manifested. If, instead 

 of drying, the material was merely stretched while wet, then again the 

 cellulose diagram appeared though not now so clearly on account of the 

 presence of water haloes. Further, they showed that if the dried bundle 

 of cotton hairs is now thoroughly re-wetted, then the cellulose diagram 

 still remains clearly present. From this they concluded that the cellulose 

 organization in the original fresh tissue was not such as to give an X-ray 

 diagram, i.e. was not an association into the crystalline regions we have 

 called micelles. In fact they went further than this. Since adult cotton 

 hairs behave in precisely the same way, they denied the presence of these 

 crystalline regions even in the fresh secondary walls. 



Clearly, however, such an interpretation of these various diagrams 

 cannot in the least be regarded as final. In the first place, the absence 

 of an X-ray diagram does not at all imply that there are no crystalline 

 regions but merely that those which do occur are too small in width 

 (estimated to be somewhat less than 20 A.) to give a crystalline pattern. 

 More seriously than this, however, the authors evidently paid too little 

 attention to the possibility that the cellulose diagram in fresh material 

 was being masked by the water haloes. This might readily explain the 

 whole series of observations, particularly since in the fresh material the 

 lumina of the hairs would be full of water, whereas in the dried, re- 

 wetted, sample they would probably be collapsed. Observation of 

 other material has, in fact, led to a conclusion quite opposite from that 

 of Berkeley and Kerr. 



As regards the condition obtaining in the thicker secondary wall, it 

 was clearly desirable to repeat these observations on cells with walls so 

 thick and so well crystalline in the dried condition that the water haloes 

 had little chance of masking any diagram in fresh material. Perusal of 

 this book will show that the alga Rhizoclonium was admirably suited to 

 this purpose. Using this material, it was found that samples taken 

 straight from the pond, photographed without drying and kept wet 

 with running water during the whole of the exposure, yielded precisely 

 the same diagram as did the same sample after drying (56). This 

 disposes at any rate of thegenerahzation ofthe interpretation of Berkeley 

 and Kerr. With primary walls, similar observations proved impractic- 

 able, presumably on account of the high water-content of growing 

 tissues in terms of the amount of cellulose present. Nevertheless with 

 conifer cambium it has been shown that, while fresh cambium photo- 

 graphed wet gives only water haloes, the same tissue photographed in 



