Vascular cambium development in sphenophyllum: A carboniferous arthrophyte

Abstract

An unusual mechanism that provides for circumferential enlargement of the vascular cambium is described in Sphenophyllum, a Carboniferous (Pennsylvanian) arthrophyte. Through an analysis of serial transverse preparations obtained from anatomically preserved material, it is demonstrated that there is a marked increase in tracheid length from the inner to the outer wood. This fact, combined with the absence of any evidence for the anticlinal division of fusiform initials, suggests that circumferential enlargement of the vascular cambium occurred through the elongation of apically intrusive fusiform initials. Compared to other plants, both extant and fossil, the secondary tracheids in Sphenophyllum are the longest conducting elements that have yet been described.