428 Dr. W. L. Balls and Mr. H. A. Hancock. 



The Primary W all. 



Various details of our evidence confirm the view that this wall, even when 

 adult, is a different cellulose from that of the secondary wall. Further, we 

 have seen reason to helieve that until growth in length has passed its 

 maximum rate, the cellulose (as distinct from the cuticle) has a different 

 composition from that which it has assumed when the secondary thickening 

 begins. We ourselves, for convenience, called this early stage " pre-cellulose," 

 and we have since learned* that the general problem is now being investi- 

 gated by Priestley. Accidentally, our preparations have shown the secondary 

 cellulose completely dissolved, but the primary wall, spirally marked, 

 untouched. 



The pit spirals of the secondary wall (see below and figs. 5-7) are con- 

 tinuous through the primary wall, and possibly even to the cuticle spirals 

 (vide supra). Thus it would seem that the law of Predeterminationf plays 

 an important part in the cotton hair, and the bearing of this on our convolu- 

 tion maps will be described later. 



The objects discovered and excellently photographed by De MosenthalJ we 

 propose to designate as the " slow spirals." Their nature is obscure, but they 

 are evidently a kind of pitted corrugation in the outer surface of the primary 

 wall, to which the cuticle moulds itself. The sides of the trough in which 

 the elliptical craters lie often project beyond the surface of the hair, and are 

 thus discernible in profile. These slow spirals are particularly easy to see in 

 fuzz hairs, but are probably present to some degree along all parts of every 

 hair, lint (fig. 3), or fuzz, for they flash out momentarily during swelling with 

 critical-strength sulphuric acid, even though not visible previously. The 

 spiral shows frequent reversals (fig. 3). The relation of this spiral to the 

 pit spirals, in respect of pitch, direction, and reversals, has been studied in 

 detail, and we have satisfied ourselves — with some regret for an untenable 

 hypothesis — that they are sometimes independent of one another. We have 

 no evidence that the slow spiral pattern is pursued into the formation of the 

 secondary wall, unlike the pit spirals, nor even that it represents any textural 

 modification (as distinct from modification of surface or thickness) in the 

 primary wall itself, excepting that when a hair has been " tendered " by acid it 

 shows a saw-tooth form of cracking, the long slope coinciding with pit spirals 



* Discussion in Section K on the "Quantitative Analysis of Plant Growth," ' British 

 Association,' 1921. 



t W. L. B., "Predetermination of Fluctuation, a Preliminary Note," 'Proc. Cam- 

 bridge Phil. Soc.,' May, 1914. 



+ Loc. cit. W. L. B., " Analyses of Agricultural Yield," Part III, « Phil. Trans.,' B, 

 vol. 208, p. 157 (1917-18). 



