94 



FUNDAMENTALS OF SUBM IC RO S C OP I C MORPHOLOGY 



are only possible if several particles aggregate. It is unlikely, however, 

 that the aggregation affects fully folded globular particles; probably 

 they become deformed and partly unfolded by the flow gradient, so 

 that somewhat expanded macromolecules aggregate. 



Micellar textures. Some examples will demonstrate the results ob- 

 tained so far in the optical structure analysis of gels (Frey- Wyssling, 

 1930). The majority of gels to be considered possess a micellar frame- 

 work containing regions of lattice order with rod-shaped crystals. In 

 the following schemes these are indicated by dashes, although it 

 should be remembered that these lattice regions do not represent 

 isolated dispersed particles but that they are all interlinked and inter- 

 woven by chain molecules. 



When it has been ascertained by a combination of optical results and 

 X-ray analysis, or birefringence of flow, that the rod-shaped lattice 

 regions or the chain molecules are optically positive with respect to the 

 longitudinal axis, the orientation of the lattice regions can be derived 

 from the character of the double refraction in various sections of the 

 gel. This can be demonstrated in particular in the case of all walls ot 

 anisodiametric plant cells. As shown in Fig. 65, the orientation of 

 the lattice regions is indicated by the arrangement of index ellipsoids 

 in radial, tangential and cross-section. 



In the secondary wall of a bast fibre the lattice regions run almost 

 parallel to the axis {fibre texture. Fig. 65a). If their orientations are 

 scattered with respect to the cell axis, the cross-section which in the 

 first case is almost isotropic becomes birefringent ; we obtain a fibroid 

 texture (Fig. 65b). The counterpart of the fibre texture is the ring 

 texture (Fig. 65c), in which all lattice regions run in tangential orienta- 

 tion. This texture occurs in the ring-shaped reinforcements of young 

 vascular cells. If, starting from this texture which is optically negative 

 with respect to the cell axis, the lattice regions are allowed to scatter, 

 the widespread tube texture is obtained (sieve tubes, latex tubes, vessels, 

 elongated parenchyma cells, etc.). Here the tangential section is optic- 

 ally negative; the radial section, however, is positive, since all projec- 

 tions of the scattered rod-shaped lattice regions upon the radial section 

 are approximately parallel to the axis. As there is a continuous change 

 from the negative region to the positive one, a front view of these 

 cells will show an isotropic zone in which the two regions of opposite 

 sign become merged (Fig. 65d). 



