Internodal Vascular Strands of Equisetum. 11 
PHYLOGENETIC CONSIDERATIONS 
ON THE 
INTERNODAL VASCULAR STRANDS OP EQUISETUM , 
By Isabel M. P. Browne. 
[With Seven Figures in the Text] . 
T HE descriptions in the text-books of the vascular strands in 
the internodes of Equisetum are somewhat meagre and 
inadequate. In discussing the structure and nature of these 
strands it will be convenient provisionally to use the word bundle 
for them individually, without thereby prejudging their morpho- 
logical nature. 
Campbell (5, p, 464) figures such an internodal bundle of the 
aerial shoot, probably of E. maximum , Lam., for in the figure are to 
be seen the conspicuous tannin cells characteristic of this species. 
His drawing shows very clearly not only the carinal canal, with the 
remains of the carinal group of protoxylem adhering to its margin, 
but also the two lateral groups of metaxylem, situated near the 
periphery of the bundle and separated from the carinal canal by 
five or six cells. Curiously enough, his description makes no 
mention of these lateral groups of metaxylem. A rather fuller 
account of the internodal vascular bundles, including a description 
of the well-known carinal group of protoxylem and the two separate 
lateral groups of metaxylem, was given by Professor Bower (p. 386 1 ) 
in his Origin of a Land Flora in 1908. Professor Bower in his 
description and discussion uses the word axis and of his three 
figures of internodal bundles, copied from Pfitzer in Rabenhorst’s 
Kryptogamen-Flora, two are from the rhizomes of Equisetum 
litorale t L., and E. silvaticum , L., and the third from the aerial stem 
of E. palustre , L. His description, though brief, is thus a general 
one. It may perhaps be pointed out that the words internodes of 
the axis cover a wider field than that to which Professor Bower’s 
description applies. The bundles of the subterranean tubers and 
those of the primary axis are also, in part of their course, inter¬ 
nodal axial bundles and Professor Bower’s description is inappli¬ 
cable to them. 
Subterranean tubers have been recorded from several species, 
and figures of their vascular bundles have been published for 
E. arvense by Milde (12, PI. 1, Fig. 22) and by Ramey (15, PI. 6, 
1 The small white space in the metaxylem-group on the reader’s left is 
an intercellular space, not a parenchymatous cell. 
