Helical Thickenings and Micellar Orientation in the Secondary Wall of Conifer Tracheids

Abstract

THE suggestion that the cytoplasmic surface possesses the capacity to govern the micellar orientation of the cell wall has been made both by Frey-Wyssling¹ and Preston², whereas the possible influence of forces arising from cell turgor and protoplasmic streaming have been discussed by Castle³ and by van Iterson⁴. Difficulties in technique have prevented any direct experimental proof of either hypothesis. The formation of cell-wall thickenings which are present in the prosenchyma of many plants has, however, been shown by Cruger⁵ and others⁶ to reflect a structural differentiation in the cytoplasm of a pattern similar to that of the later-formed thickenings, and recognizable upon plasmolysis. In conifer tracheids the phenomenon has been illustrated diagrammatically by Jeffrey⁷, although it is not clear whether his diagram was based on direct examination or analogy with other cells. These observations, however, point clearly to the influence of the cytoplasm in governing the orientation of cell-wall thickenings, to the axis of which the micelles of cellulose are parallel⁸. As the thickenings are an intrinsic part of the cell wall, and in view of the cytoplasmic differentiation which precedes their development, it becomes of interest to consider whether further evidence can be obtained to indicate a similar function of the cytoplasm in governing micellar orientation in the cell wall generally.