26 o 
Browne . — 77 /<? Anatomy of the 
the members of this whorl became obsolete at a relatively early period in 
the phylogeny of the genus, and that E. xylochaetum and E . giganteum are 
descended from forms in which the annulus normally contained no vascular 
bundles. In fact, though the annulus is a whorl of reduced leaves, the traces 
found in the two species just mentioned are not regarded as strictly homo- 
logous with the traces of the other leaves. Such a view would help us to 
understand why no fresh parenchymatous meshes are developed above the 
annulus of E. giganteum : the formation of additional vascular elements 
(the annular bundles) proved a considerable strain on the powers of xylem 
production, and one result was an insufficiency of xylem above the node to 
allow of the formation of fresh parenchymatous meshes. On this view, too, 
we should not be confronted with the difficulty of homologizing the annulus 
with a whorl of sporangiophores, a difficulty which it is hard to see how to 
overcome if the annulus be regarded as primitively sporangiferous. 
Summary. 
1. If we were to arrange the cones of the species of E guise turn , the 
anatomy of which is known to us, in a series showing gradual reduction of 
the vascular system, we should place the species in the following order : 
(i) E. arvense , (2) E. hyemale , (3) E. patustre , (4) E. giganteum , (5) E. 
maximum , and (6) E. limosum. In this series, which must not be regarded 
as a phylogenetic sequence, the first species possesses, relatively to its size, 
by far the best developed, and the last two species by far the most reduced 
vascular systems. In the second, third, and fourth species the reduction of 
xylem has proceeded in somewhat different ways, but, on the whole, the 
vascular system of the cone has reached much the same degree of 
reduction. 
2. The reduction of the xylem of the cone is manifested in E. hyemale 
and in E. giganteum , as in the other species studied, by the persistence of 
parenchymatous meshes, arising vertically above traces that have departed, 
upwards into more than one internode, and by their extension laterally 
above traces given off from at or near the edge of a strand. Both 
phenomena may be considered to be due to poor development of axial 
xylem at the nodes of the cone. 
3. Specially characteristic of E. hyemale and showing relatively good 
development of the vascular system are the following points : (a) the 
closure of parenchymatous meshes by the formation of additional tracheides 
at the node rather than by the oblique course of the tracheides of the 
branches of a strand above the departure of a trace ; (b) the relatively large 
number of parenchymatous meshes and the high proportion ^mong these of 
meshes of the first and second orders. 
4. Relatively high development of the xylem of the cone of E . gigan- 
teum is shown : ( a ) by the slightly greater radial extent of the xylem in this 
