290 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES HE 



This means to say that elastic cell extension, instead of giving wa^r 

 to the lateral tension, follows the weaker longitudinal stress. 



Castle (1937b) thinks that the larger tangential stress favours the 

 transverse orientation of the cellulose strand and thus causes the 

 tubular texture. Careful examination of Fig. 140 (p. 284), however^ 

 leads one to conclude that no such mechanistic process can explain 

 the very complicated facts of the submicroscopic morphogenesis 

 which is observed. 



CoRRENS, who noted the predominance of lateral stress in cylindri- 

 cal cells as far back as 1893, came to the conclusion that "the existing 

 stressing effects" in the micellar texture of laminated membranes of 

 filiform algae "cannot be responsible for their orientation" (1893,. 

 p. 284), since laterally and longitudinally orientated systems occur 

 alternately. 



A further argument which proves the relative unimportance of the 

 turgor pressure in growth problems is the study of energetics during 

 cell elongation. Assuming the elongation to be really an elastic stretch, 

 which is later fixed by intussusception, the work involved in wait 

 extension can be calculated (Frey-Wyssling, 1948a, b). It turns out 

 that this work is only i/iooo to i/ioo of the total energy produced b}~ 

 the cell when the sugar content of its vacuolar sap is respited. For 

 this reason, there must be other fundamental processes, such as- 

 transport of substances and biosynthesis, which cause growth, and the 

 problem of morphogenesis remains as enigmatic for submicroscopic 

 morphologists as it was for microscopic cytologists. 



The secondary cell wall. According to Van Iterson (1927) the sub- 

 microscopical texture of the secondary cell wall depends on the 

 direction of flow of the protoplasm depositing the laminae of ap- 

 position. Currents of protoplasm can, in fact, be observed to circulate,, 

 depositing rings or bars during vascular formation. Van Iterson 

 (1937) furthermore tries to explain the direction of flow causally. It 

 is, he says, principally axial in the staminal hairs of Tradescantia, for 

 example, since, owing to the tubular texture of the cellulose mem- 

 brane, the cells tend to elongate. However, the outer cuticular layer 

 with fibrous texture impedes extension, but there is pronounced elon- 

 gation the moment the cuticularized outer layer of withered flowers 

 bursts. On the basis of these observations it was inferred that, owing 

 to the tubular texture of the primary wall of embryonic fibres, the 



