CHAPTER XXVIII. 
SPORANGIOPHORIC PTERIDOPHYTES. 
I. EQUISETALES. 
Unper the common designation of the “Sporangiophoric Pteridophytes” 
may be grouped together those forms whose sporangia are disposed, either 
singly or in larger numbers, upon more or less elongated vascular stalks, 
which are enlarged as a rule at their distal ends. The existence of the 
sporangiophore clearly distinguishes these plants from the Lycopodiales, 
though it may for the present remain an open question whether any 
genetic connection existed between the latter and the sporangiophoric types. 
Under this designation are included the Fquisetales and the Sphenophyllales 
(incl. Psilotaceae), while, according to the view which will be developed 
below, the Ophioglossales will also appear as an outlying group sharing 
the same character, though in a more elaborated form. It will be a 
matter for later discussion how far the existence of the sporangiophore 
as the immediate spoyangium-bearing member will supply a valid basis 
on which to trace affinity: the decision must rest on the degree of 
correspondence of the sporangiophoric types in other characters, such as 
the external morphology and anatomy of the vegetative organs, and the 
details of the gametophyte. Unfortunately these are often so imperfectly 
known that we are thrown back in great measure upon the spore-producing 
members: but on grounds previously explained these are held to be the 
most important of all. 
The Equisetales, which are taken first of the sporangiophoric types, 
are distinguished from the rest by the fact that their sporangiophores are 
inserted directly upon the axis, not on appendicular parts: in some 
cases they show a definite relation to the bracts which subtend them: in 
others no such relation exists. Other less distinctive characters of the 
vegetative organs are the constantly radial construction of the shoot: 
the elongation of the internodes which are longitudinally striated, the 
verticillate arrangement of the leaves, a high degree of branching, and a 
structure of the stele with a ring of isolated vascular strands; these 
