1. The general internal structure of the stem of Angiopteris evecta consists of two main regions, the cortical and central vascular. The relatively thick cortex is traversed by leaf traces and roots. The central region consists of a vascular strand which appears crescent-shaped in cross-section and is imbedded in a central parenchyma tissue. This strand gives off root steles and leaf traces. In addition, commissural and medullary strands appear in the central region. 2. The leaf traces are given off from one edge of the central strand, and this contribution is always from the same edge in the same plant. On about the same level that the leaf trace leaves the central strand a root is attached on the outer side of the other edge. The contribution thus made to the leaf traces is made good on the opposite edge in two ways, by an increase in the vascular tissue on the edge itself, and by the addition of commissural strands. 3. The commissural strand originates from the free edge of the leaf trace after the lat...