Anatomy of the Cone and Fertile Stem of Equisetum . 697 
favourably considered by Scott (Scott, pp. 158-62) \ Lignier (Lignier), 
Jeffrey (Jeffrey ( 1 ), p. 185), and others. Bower, however, was strongly 
opposed to it, regarding the sporangiophore as an organ sui generis , not 
only in the Equisetales, but also in the Sphenophy Hales (Bower ( 2 ), pp. 381-4), 
while Seward supported him as far as regarding the sporangiophore, at least 
provisionally, as an organ sui generis (Seward, p. 15). There are certainly 
much stronger reasons for doubting that the sporangiophore represents a lobe 
of a leaf in the Equisetales than in the Sphenophyllales. In the former 
group we are at once met with the difficulty of explaining those cones in 
which the bracts are either absent or present only at considerable intervals. 
Those that regard the sporangiophore as a lobe believe that it has been 
displaced in Calamostachys ; some years ago Dr. Scott pointed out that if 
such displacement occurred in a form in which, as in Sphenophy llnm fertile , 
both lobes of the sporophyll bore sporangia, we should get a near approach 
to the Eqnisetum arrangement (Scott, p. 162). Jeffrey also remarks that there 
are many reasons for regarding the sporophyll in the Equisetaceous series 
as dorsiventrally lobed. He suggests that in this case the sporangiophores 
of Equisetnm represent the result of fusion of ventral and dorsal segments, 
or that they are ventral segments, the dorsal having become obsolete. 
No known cone seems to show such an obsolescence of bracts, and the 
sporangiophores of Eqnisetum do not seem to be dorsiventrally double. 
I was at first inclined to accept Dr. Scott’s tentative suggestion that in 
Equisetum each sporangiophore might represent a separated lobe of a dorsi- 
ventrally lobed sporophyll ; in this I was influenced by the analogy with 
the Sphenophyllales, but principally by the fact that I felt unable to escape 
the conviction that the sporangiophores of Archcieocalamites are the homo- 
logues of those of Catamites , and these sporangiophores seem very closely 
to resemble those A Equisetum (Browne, p. 16). But a comparative study 
of the cone of Equisetum seems to show that the sporangiophores are whole 
appendages and that their insertion marks the position of a node. It is 
true that though the cone has more internodal xylem than the stem, the 
ring of wood at a fertile node is only exceptionally complete ; such a ring 
is, however, by no means rare in E. arvense. Moreover, at the insertion of 
the whorled appendages there is (except in cases of great reduction of the 
xylem) a marked increase in the amount of xylem, leading to the formation 
of bands or of a ring of xylem. Above the departure of the traces of the 
sporangiophores, and often very much at the same height as the breaking 
up of the xylem above the leaf-traces, these bands or this ring of xylem 
breaks up owing to the appearance of parenchymatous meshes. 2 In this 
1 Dr. Scott subsequently pointed out that the spore-bearing organ might be a whole leaf or a lobe 
of a leaf (Studies in Possil Botany, 1909, p. 623). I have been led to adopt this view. 
2 The nodal xylem of the stem of course differs markedly from the xylem at a fertile node, for, 
except for the protoxylem, it consists ol large reticulate elements and has a considerable depth radially, 
while the xylem at a fertile node consists entirely of relatively small annular and spiral tracheides 
and is very narrow radially. 
