A Unit of Construction in the Ptcridophyta. 143 
THE SPORANGIOPHORE—A UNIT OF STRUCTURE IN 
THE PTERIDOPHYTA. 
By M. Benson, D.Sc. 
[Text-Figs. 25, 26.] 
O NE of the many contributions to our knowledge of the phylo- 
geny of the Vegetable Kingdom that are due to Palaeobotany 
is the conception of the structure known as a sporangiophore. 
As far back as 1900 Dr. Scott brought together in the first 
edition of his “ Studies in Fossil Botany ” a series of facts pointing 
to the wide occurrence of such a body and the great range of form 
which it might assume. 
The number of types known to us has now greatly increased. 
The range of form in the Sphenophyllales may be from a tetra- 
sporangic to a monosporangic condition ; from a sessile to a pedi- 
cillate; it may be inserted on a bract or on an elongating axis. 
In the Equisetales it may be tetrasporangic or polysporangic. 
It is generally radially symmetrical, but in the forms known as 
Stachannularia and Cingularia it is dorsiventral. It may appear 
associated with sterile bracts or without them, but is always 
inserted directly upon the elongating axis. 
In the Psilotales the sporangiophore may be bi-sporangic or 
tri-sporangic. In this recent group variations have also been 
recorded by Professor Thomas 1 and Miss Sykes 2 , which further 
accentuate the plasticity of the sporangiophore. Miss Sykes 
records cases in both Tmesipteris and Psilotum in which the 
sporangiophore is terminal on an axis, and in which the structure 
is monosporangic. 
The three sub-phyla thus far referred to are sometimes grouped 
together under the name “ Sporangiophoric Pteridophyta,” as, for 
instance, by Professor Bower in Chapter XXIX. of his “ Origin of 
a Land Flora.” In the succeeding chapter, however, he uses the 
term “ sporangiophorefor the fertile part of the leaf of the 
Ophioglossaceae. I will discuss the application of the term in this 
sense in a later paragraph. Yet a second problem arises in 
connection with the use of this term. It has been again and again 
suggested that we have in the Lycopodineous “sporange” a reduced 
structure which is homologous with the sporangiophore of the 
1 Thomas. Proc. R. S., Vol. LXIX. 
* Sykes. Annals of Botany, 1908, January and July. 
