304 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES III 



cleaned chitinous tendons, as they do bast fibres^ dichroically; the 

 direction of the stronger light absorption coincides, as in cellulose, 

 with the fibre axis. The similarity in the dichroic coloration of chitin 

 and cellulose is interesting in that it tends to show that the dichroism 

 of these colour reactions characterizes not so much a certain chemical 

 compound as its micellar structure with orientated inner surfaces. 



The egg-shell of ^j-^r^m provided Schmidt (1936) with an object 

 in which the submicroscopic chitin rodlets scatter, thus forming a 

 wall of foliate texture. The plan ot the eggs shows them to be isotropic, 

 but the optical cross-section through the wall exhibits a negative 

 spherite cross. This optical behaviour is produced by an arrangement 

 of the submicroscopic ordered lattice regions as represented in Fig. 1 48c. 



The sporangiophores of Aspergillus niger must, from their optics, 

 be presumed to have a fibroid texture with scattering (Fig. i48d; 

 Frey, 1927a). We do not 3^et know, however, whether this membrane 

 is stratiform like Phycowjces; for in that fungus, with particularly large 

 sporangiophores several centimetres in length, Oort and Roelofsen 

 (1932) found an outer primary skin of tubular texture, under which 

 there is a thickened secondary wall layer of fibrous texture exhibiting 

 slight scattering; it is by reason of its predominant bulk that only this 

 appears on the X-ray photograph. It is assumed that at the core there 

 is another, very thin layer of steep spiral texture (Fig. i48e). 



These results of the indirect methods are only partly corroborated 

 by the electron microscope. The cell wall of the sporangiophore of 

 Phycomyces consists of chitinous microfibrils which are similar to those 

 in cellulose walls (Frey- Wyssling and Muhlethaler, 1950; Roelof- 

 sen, 195 la). There is a homogeneous cuticle devoid of any structure, 

 a primary wall with interwoven microfibrils and a thick parallel 

 textured secondary wall (Fig. 86c, p. 128). Roelofsen differentiates 

 the primary wall in an outer layer with a network texture and an inner 

 layer with almost transverse oriented microfibrils. The texture of the 

 uniform secondary wall runs almost parallel to the cell axis. There is 

 no pronounced spiral texture and no special internal wall layer as had 

 previously been found in the polarizing microscope (Fig. 1486). 



Spiral growth. The end of the sporangiophore is conspicuously of 

 spiral growth (Oort, 193 i; Castle, 1937a, 1942). This fact can be 

 verified by placing a mark above the zone of growth which was found 

 ^ Walchli (1945). 



