38 A. C. Seward. 
ON THE SO-CALLED PHLOEM OF LEPIDODENDRON. 
By A. C. Seward, F.R.S., 
University Lecturer in Botany, Cambridge. 
(TEXT-FIGURES I. AND II.) 
f^INCE the publication of a paper by Witham of Lartington in 
1832 “On Lepidodendron Harcourt'd',” the anatomical inves¬ 
tigation of the various types of trees and other plants that constituted 
the forests of the Coal-period has made rapid strides, more 
particularly during the last thirty or forty years. The genus 
Lepidodendron is one of the commonest and best known members of 
the Upper Carboniferous flora of the northern hemisphere, and we 
possess a fairly extensive knowledge of the structure of several 
distinct forms. One result of the more minute anatomical study 
has been to bring to light certain features, which tempt us to 
speculate on the environment of the Palaeozoic plants. There is a 
fascination in endeavouring to utilise anatomical facts as indices of 
external conditions; a closer acquaintance with the structure of the 
plants’ machinery enables us to revivify the tissues of petrified 
fragments, and to consider them as portions of a working machine, 
impelled by the same forces and working towards the same ends 
that govern the life-functions of living plants. In some respects 
the organization of the extinct types was not strictly according to 
the pattern which our knowledge of living plants has led us to regard 
as typical; our aim is, to be in a position to answer the question— 
was the physiological division of labour in a Lepidodendron stem 
essentially similar to that which we find in the nearest living 
representatives of the genus ? 
I wish to confine myself in the present article to one or two 
points, and to discuss as briefly as possible certain structural 
features, interpreted by some writers as being in accordance with 
modern types, but which I believe illustrate peculiarities in the 
mechanism and physiology of Lepidodendron stems. 
We will restrict ourselves for the present to two species, 
Lepidodendron fuliginosum Will, and L. Wunschianum Will. 3 In 
Lepidodendron fuliginosum the stem possesses a single stele consisting 
of an axial mass of parenchyma surrounded by a cylinder of primary 
xylem, which becomes encircled, at an early stage in the growth of 
1 Witham, 1832. ‘ On Lepidodendron Harcourtii,” Trans. Nat. Hist. 
Soc , Neivcastle-upon-Tyne , 1832. 
2 These two species belong to the Lepidophloios section of 
Lepidodendroid plants. 
