THE STRUCTURE OF PROTOPLASM 



255 



Polarization studies on the cell walls of plants have been 

 made by Frey-Wyssling. The method is that of immersion 

 in liquids of known index of refraction. When a crystal is 

 immersed in a liquid the index of refraction of which is equal 

 to that of one of the three indices of the crystal, then the bound- 

 ary between liquid and crystal, viewed in the light furnished 

 by Nicol prisms, disappears when the plane 

 of polarized light is in line with the direction 

 of that particular crystal index which is 

 identical with the index of the oil. A series 

 of mixtures of amyl-benzyl alcohol and 

 cinnamon clove oils of increasing refractive 

 indices were used. In this way, Frey- 

 Wyssling established the three main indices 

 of refraction na, w/S, and ny (Fig. 135). By 

 these means, he showed that in cell walls 

 there are submicroscopical (colloidal) rod- 

 shaped particles which he identifies with 

 the Nageli micelles. The long axis of the ^j^, 135.— Orienta- 

 micelles corresponds to the direction of the tion of the indices of 



P ,. . , , 1 1 ii 1 refraction in plant-cell 



greatest retractive mdex; the latter value, ^aUg {From Frey- 

 therefore, gives the orientation of the micelles WyssUng.) 

 in the wall. 



Photographs of cellulose taken with the Spierer lens (page 98) 

 add further evidence to the general conclusion that cellulose 

 possesses a colloidal structure of symmetrically arranged rods. 

 The lens reveals parallel striae (Fig. 136A) which appear to be 

 composed of microscopic units oriented end to end. These 

 units are about 2 /x long and were consequently termed super- 

 micellae to distinguish them from the ultramicroscopic micellae 

 postulated by Nageli and now generally accepted by chemists as 

 the unit of colloidal structure. But as the cellulose molecule 

 apparently reaches the microscopic length of 1.7 n, then the 

 supermicellae become micellae in the strict sense, for the latter 

 by definition are bundles of molecules; both must, therefore, 

 be of the same length. 



The striae (Fig. 136 A) which are built of rod-shaped super- 

 micellae oriented end to end in continuous or discontinuous 

 lines are in parallel arrangement and thus form lamellae, or 

 plates, which in their turn combine to produce the mass of 



