x] ON GEODESICS 747 



or embryological growth. But the spiral thickenings in the woody 

 fibres of a plant are of another order of things, and lie in the region 

 of molecular phenomena. The delicate spirals of the cell-wall of 

 a cotton-hair are based on a complicated cellulose space-lattice, 

 recaUing Nageh's micellar hypothesis in a new setting; and giving 

 us a glimpse of organic growth after the very fashion of crystaUine 

 growth, that is to say from the starting-point of molecular structure 

 and configuration*. 



* W. Lawrence Balls, Determiners of cellulose structure as seen in the cell-wall 

 of cotton-hairs, Proc. R.S. (B), xcv, pp. 72-89, 1923, and other papers. Cf. also 

 Wilfred Robinson, Microscopical features of mechanical strains in timber, and the 

 bearing of these on the structure of the cell-wall in plants, Phil. Trans. (B), ccx, 

 pp. 49-82, 1920. 



