Fine Structure of the Plant Cell Wall

Abstract

ALTHOUGH it is almost eighty years since Nägeli¹ introduced the micellar hypothesis to account for the anisotropy of certain plant structures, it is remarkable how nearly his original conception satisfies the most recent discoveries. It may be recalled that Nageli pictured the cell wall as composed of ultra-microscopic particles to which he gave the name 'micelles', and which were regarded as discrete units, more or less like the bricks in a masonry wall. In order to explain the shrinkage of wood it was assumed that water entered or left the intermicellar spaces, pushing the micelles farther apart or allowing them to come nearer together, and the elongated shape of the micelles was held to account for the difference between longitudinal and transverse shrinkage; the optical anisotropy of the cell wall was referred to the optical properties of the micelles themselves. Some revision of Nageli's statement was however found necessary, and a large body of workers rejected the conception completely, postulating instead a system of continuous or connected cellulose threads or layers. Neither conception is completely satisfactory and the modern tendency is to seek a compromise between the two. The position has been reviewed from the point of view of physicist, chemist and botanist^2,3,45, perhaps the fullest summaries being those of Frey-Wyssling^5*, which have been freely used in the present account.