96 FUNDAMENTALS OF S UBM I C RO SC OP I C MORPHOLOGY I 



as shown in Fig. 66, spherites can be positive or negative both with 

 radial and with tangential arrangement of the structural elements, 

 depending on whether the structural elements themselves are positive 

 or negative with respect to their axis. Hence the first thing to ascertain 

 is the optical character of these structural elements. In most cases the 

 texture is as shown in Fig. 66a (starch grains, inulin). 



Fig. 66. Gels with spherite texture, a) Positive, b) negative spherite of positive 



rodlets; c) negative, d) positive spherite of negative rodlets; e) positive myelin 



sphere (oblate) of positive rodlets. 



In hollow spheres, the reference axis cannot be determined with 

 certainty. In isodiametric parenchyma cells, for instance, the double 

 refraction of the cell wall is referred to the tangential direction (Fig. 

 63e, p. 87), in analogy to the situation in anisodiametric cells, 

 although they are isotropic in radial direction. This is due to random 

 orientation of the structural elements in the tangent plane. An arrange- 

 ment of this kind is designated as foliate texture. For further details 

 of optical texture analysis we must refer to the literature concerned 

 (Ambronn and Frey, 1926; Frey, 1926b; Frey-Wyssling, 1930, 

 1935a; Schmidt 1934, 1937a). 



b. X-ray Analysis of Gels 



Micellar strands. A complete structural analysis by means of X-rays 

 is only possible if crystalline lattice regions are present. In the case of 

 molecular colloids such as rubber solutions, protein solutions, etc., 

 irradiation with monochromatic X-rays furnishes as a rule no more 

 than an "amorphous" ring, which gives some information about the 

 /«/ramolecular periods occurring most frequently (for instance, in 

 rubber: the length of an isoprene unit). Only when the chain molecules 

 are arranged in a crystal lattice does X-ray analysis yield interference 

 phenomena rich in lines or spots, from which far-reaching morpholog- 

 ical conclusions can be derived. This will be further illustrated bv 



