VII.—The Relation of Size to the Elaboration of Form and Structure of the Vascular Tracts in Primitive Plants

Abstract

In my Presidential Address of October 1920 I cited the stems of certain Zygopterideæ in illustration of size as a factor in Stelar Morphology. But only a few salient facts were adduced from the protosteles of their stems. The relation of increasing size to the elaboration of the vascular tracts of primitive plants deserves further examination: and the results would appear the more cogent if the evidence were collected not only from series of plants which are related to one another, or even from different parts of the same plant, but also from series not so nearly related. A re-examination of the published figures of axial steles and petiolar traces in the fossil Cœnopterideæ has provided interesting results.