Vascular System of the Genus Equisetum . 221 
sections, from which diagrams of the whole vascular system were con- 
structed. 
Browne concludes that the species examined can be arranged in 
a series which shows a progressive reduction in the amount of xylem tissue. 
This ranges from a regular arrangement in E. arvense , imperfectly siphono- 
stelic at the nodes to dictyostelic in the internodes, through E. palustre , 
E. maximum , to E . limosum , where the xylem is reduced to an irregular 
network. This reduction in the xylem is accompanied by an increase in 
size of the parenchymatous meshes which separate the bundles, and in 
E. palustre these meshes often extend through the nodes, with the result 
that the vascular strands tend to run longitudinally with few anastomoses 
and are separated by relatively wide parenchymatous tracks. 
Browne describes the detailed nature of the vascular bundles, and 
draws attention to the difference between those present in the strobilus and 
those occurring in the vegetative axes. She considers that the anatomy 
of the cone axis supports the view that the sporangiophores are whole 
appendages of a foliar nature, and interprets the structure of the cone in 
terms of nodes and internodes. Browne agrees with most authors in 
regarding the annulus as a modified leaf-whorl. 
• In the present investigation cones have been prepared in the way 
already described for the vegetative organs : they were cut in half longitu- 
dinally, cleared, and stained in bulk. By this method a large number of 
specimens of different species could be prepared in a relatively short time 
and the individual variability appreciated. Both very young and mature 
cones were thus prepared in order to trace out the ontogeny of the 
vascular system. 
The first impression gained from an examination of the cone is the 
marked differences in structure it presents as compared with the vegetative 
axis. Of these the most striking are the apparent absence of lacunae, both 
vallecular and carinal, and the structure of the vascular bundles. 
Browne ( 1 , p. 684) has pointed out that instead of the three groups of 
xylem, characteristic of the bundles of the vegetative internodes, the 
bundles of the cone show a narrow tangentially extended band of tracheides, 
and suggests that ‘ in the vegetative internodes the lateral groups of xylem 
represent the free ends of a more deeply curved band of xylem, and in that 
case the position of the tracheides of the lateral groups of metaxylem in 
a radial series is due to the more or less marked curvature of a band of 
which only the carinal tracheides and the free ends are lignified. The 
primitive form of the internodal bundle would then be that of the cone.’ 
She further states (1, p. 666) : ‘. . . In a good many places there are, 
internally to the bands or ring, isolated tracheides or little groups of 
tracheides-, usually of small size ; . . . Such tracheides or groups of tracheides 
do not as a rule persist for any considerable distance in a vertical direction ; 
