The Fine Structure of Bamboo Fibres: II. REFRACTIVE INDICES AND WALL DENSITY

In the fibres of Dendrocalamus strictus and D. longispathusit has been shown that the refractive indices of the outer walllamella, parallel and perpendicular to cell length, are correlatednot only with cell length but also with the density of the wholewall. The indications nevertheless are still that the variationin refractive indices with cell length are due mainly to changesin the orientation of the cellulose microfibrils. There is,however, a subsidiary effect of factors associated with density.These factors are briefly discussed     

The Fine Structure of Bamboo Fibres: I. OPTICAL PROPERTIES AND X-RAY DATA

Following the recent work on wood tracheides and sisal fibres,a detailed investigation has been made of the fine structureof a wide variety of bamboo fibres. A combination of X-ray analysis,measurement of refractive indices in longitudinal view and ofphase differences in transverse section, has presented a completepicture of cellulose chain orientation. The wall of bamboo fibresis many layered. An outermost, thin layer is composed of cellulosechains making an angle of 35° to cell length and this isfollowed by other, inner layers where the angle steadily decreasesfrom outer to inner layers, first to about 20° and thento about 10°. These layers are separated by thicker layers,dark in transverse section between crossed nicols, in whichthe angle is seldom more than 5–6°. These are averagefigures. The results show most clearly that each angle, , varieswith the fibre length, L, in such a way that the longer cellshave steeper spirals in harmony with a relation of the typeL=A+Bcot already proposed for wood tracheides.     

Electron Microscopic Investigations of the Walls of Green Algae: I. A PRELIMINARY ACCOUNT OF WALL LAMELLATION AND DEPOSITION IN VALONIA VENTRICOSA

A survey of the structure of wall lamellae in the green algaValonia ventricosa has revealed the following details. The microfibrilsare not so constant in width as had previously been suggested;they vary in this dimension from about 100 A to about 350 A.The length of the shadow cast by separated microfibrils shadowedwith palladium-gold or with uranium suggests that the microfibrilsare flattish ribbons rather than circular cylinders. In theintermediate lamellae of the wall they are in intimate contact,probably with an interfibrillar cementing material, but in outerlamellae they become more or less widely separated. This separationis assumed to occur as a result of adjustment to size increasein the vesicle. Observation of the innermost lamella shows thatthe microfibrils here are arranged at random, in marked contrastto the condition in other lamellae. Here and there granulardeposits on this lamella appear to be connected with the cytoplasm,and it is suggested that these may represent points in the cytoplasmassociated with microfibril production. Occasional twistingof microfibrils over and around each other in most of the walllamellae suggests most strongly that the wall and the cytoplasmare not so clearly separated during deposition as has been thought.     

The Effect of Indoleacetic Acid on Cell Wall Extensibility in Avena Coleoptiles

The extensibility of cell walls in segments of living Avenacoleoptiles has been determined after treatment with IAA bythe use of a microextensometer. It has been demonstrated thatIAA has an effect both on the plastic and elastic extensibility,which is more marked if the segments are allowed to grow, exceptat temperatures nearing 0° C. The auxin-induced increasein extensibility is therefore not a direct effect on the walland metabolic factors must be involved. The results are interpreted,along cunent lines of thought, as indicating effects on thelinkage between protopectin or hemicellulose chains themselvesand between these and the microfibrillar network of cellulose.The bearing of these interpretations on the normal growth processin cell walls is briefly discussed.