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



so-called slip planes as being interrupted by the fragile middle lamella, which 

 seems improbable unless these " slip-planes " are pre-existent. The spasmodic 

 occurrence of swollen spirals in thiocyanate preparations merely showed an 

 erratic anastomosing series, but with the cuprammonium and soda mixture, 

 and better still with critical sulphuric acid (circa 1/540 sp. gr.), the nature 

 of these anastomoses was evident ; the wall is then seen to consist of about 

 a hundred spiral fibrils — a screw of a hundred threads — all approximately 

 identical, except in one respect. This exception consists in the frequent 

 presence of two spirals, within the series, which stain more deeply than the 

 others with naphthamine blue. They do not seem to be otherwise different 

 from their neighbours in any way, and as they seem always to lie at the ends 

 of the major axis of the collapsed cell-wall, they might be merely stress- 

 produced artifacts. On the other hand, one of them may disappear by 

 approaching the other, the interval between them changing. Thus, the 

 appearance shown in swollen hairs is altered from a symmetrical double screw 

 (figs. 8, 9) to an asymmetric one, and thence to a single-thread screw, as we 

 pass along the hair. This is not compatible with artifact origin, and it would 

 seem that for some reason unknown two fibrils, lying diametrically opposite 

 one another, are somewhat different from the others. We have noticed 

 similar bifurcation and re-union in the spiral thickening of protoxylem 

 vessels in other plants. 



The question of the relationship between these radial boundary surfaces 

 and the tangential growth-ring boundaries next arises. Numerous attempts 

 to demonstrate the matter clearly in transverse section have largely failed ; 

 and some considerations relating to free surface, cohesion, and the like, make 

 it rather unlikely that these two sets of structures could ever be thus demon- 

 strated perfectly and simultaneously in the swollen state. We also suspect 

 that the shearing stress of the razor edge may produce molecular disturbances 

 which alter the reactions of the cellulose. Partial demonstrations of the 

 existence of these radial boundaries have frequently been obtained, but rarely 

 (fig. 1) comparable with the growth-ring demonstration of fig. 2. We thus 

 have to depend on optical longitudinal sections, and by this means have 

 satisfied ourselves in exceptionally good preparations that the spirals are 

 arranged in layers, each layer constituting a single growth-ring. 



The cotton hair cell-wall is thus an elaborate structure, laid out on a 

 simple plan. In the first instance, a spiral pattern seems to be laid out in 

 the primary cell-wall and cuticle ; this, it should be noted, must happen while 

 the hair is growing in length. The deposits of secondary cellulose, as growth- 

 rings, do not obliterate this pattern, but follow it most strictly. Thus, a radial 

 (spiral) structure persists through the concentric deposits. The simple pits 



