450 Browne. — A Fourth Contribution to our Knowledge of 
out, and it is abundantly confirmed in this investigation, that the gap does 
not, except in a few cases, occur immediately above the point of departure 
of the trace ; and most frequently shows no relation to it. 5 (Barratt, p. 231.) 
Barratt’s own view on the determining factor in the distribution of 
parenchymatous meshes is given as follows on p. 227 of her paper : e It is 
suggested that the determining factor in the relative development of the 
metaxylem, and hence of the meshes, is primarily a mechanical one. It is 
significant that the species with large and heavy cones have more abundant 
xylem and more regularly developed network.’ 
The first point that I should like to emphasize in connexion with the 
above quotations is that I have never regarded the parenchymatous tracts 
of the cone as foliar gaps, or even as gaps left by the traces of the sporangio- 
phores. In my first paper treating of the cone of Equisetum I especially 
pointed out that the parenchymatous meshes of the axis of the cone, like 
those of the vegetative axis, do not, except at the reduced or immature apex 
of the cone, originate immediately above the traces, and that they are not 
foliar gaps as defined by Jeffrey (Browne ( 1 ), p. 698). I proceeded to com- 
pare these meshes with the tracts of parenchyma that originate some way 
above the traces of certain Osmundaceae, and pointed out that these 
Osmundaceous parenchymatous tracts were not, when the)' originated some 
way above the trace, foliar gaps. I held that the structure now found in the 
axis of the cone of Equisetum was derived from a siphonostele, a view with 
which Barratt has expressed agreement. I further suggested that in 
the phylogeny the parenchymatous meshes probably arose in the internodal 
region vertically above traces — not a surprising position when we remember 
that the current of water, some of it being deflected into the sporangiophores, 
would be diminished above the departure of the traces. But I especially 
added that the cases in which the mesh arose closer to the trace were 
probably instances of the reduction of xylem (Browne ( 1 ), p. 699). In fact, 
it was to emphasize the point that the parenchymatous tracts of the cone 
were not foliar gaps that I distinguished them by the term mesh. 
Barratt’s statement that the meshes of the cone most frequently show 
no relation to the departure of the traces seems to me unjustified. An 
examination of the reconstructions of complete steles of the cones of 
E. arvense , E. palustre , E. limosum (Browne ( 1 ), Text-figs. 1, 3, 5, and 6 ), 
E. maximum (Browne ( 2 ), Pis. XII and XIII), E. hyemale , E. gig anteum 
(Browne ( 3 ), Text-figs. 2, 3, 4, 5, 6, and 7), E . sylvaticfim and E. variega - 
turn (Text-figs. 1, 2, 8, 9, and 10 of the present paper) will show that in by 
far the greater number of cases meshes originating within the cone do show a 
relation to the point of departure of a trace ; for, in the great majority 
of cases, these meshes arise vertically above the departure of a trace of the 
node below, though at a varying height above this node. In E. debile 
(Text-figs. 3-7 of the present paper) few meshes originate within the cone 
