STUDIES IN GELS 



95 



If the lattice regions do not scatter, but deviate from the direction 

 of the cell axis while remaining parallel to each other, a spiral texture 

 is obtained, as occurs in cotton wool fibres, the tracheids of conifers 

 (Jaccard and Frey, 1928; Preston, 1934, 1946) and the wood fibres 

 of deciduous trees. 



H-'^ 



-j-""? 



riy ny 



o) 



+ 



ii/mi 



nil 



c| l|l, 



lllll« 



l/lIU 

 llllll 

 lllllll 

 llllll 

 llllll 

 lllllll 

 l''l|l| 

 IHllU 

 ll'll'l 

 llllll 

 II Ml 

 Ill/Ill 



III' 

 ll>llil 



+ + 



'"'lllllll 



// 'INN 



■A 



« 



i/,i /i\ 



i;:('* 



/\<\ii llllll 



'llill' V ,7) \i 



11111/ 

 llllll 

 lllllll 



!ll| 

 lllllll 

 llllll 

 mm 



nil 

 iilVii 

 lllllll 

 mil 

 lllllll 

 iiiii 



mini 

 'mil 



1 mil 

 nil; 





Hy fly 



c) 



^.V-i-'n'y 



d) 



Fig. 65. Micellar textures of cell walls (from Frey-Wyssling, 1930). 

 a) Fibre texture, b) fibroid texture, c) ring texture, d) tube texture, n^ biggest, 

 Hq smallest refractive index of cellulose; n^* biggest, n^* medium, n^* 

 smallest refractive index of the cell wall, i isotropic, -f optically positive, 



— optically negative. 



In isodiametric objects there exists no morphological axis which may 

 serve as reference axis to the double refraction. In spherical objects 

 such as starch grains, spherites and the like, the radial direction is 

 therefore chosen as reference axis. If the refractive power for vibrations 

 parallel to this axis is larger than that for vibrations in a tangential 

 direction, the spherite texture is called positive; in the opposite case 

 it is called negative. The determination of the optical character of a 

 spherite built up of chain molecules or rod-shaped lattice regions, 

 however, does not sufhce to derive its submicroscopic texture. For, 



