The Sporangiophore‐a Unit of Structure in the Pteridophyta.

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 flrst 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 tetrasporangic to a monosporangic condition ; from a sessile to a pedicillate; 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 Psiiotales the sporangiophore may be bi-sporangic or tri-sporangic.In this recent group variations have also been recorded by Professor Thomas' and Miss Sykes', which further accentuate the plasticity of the sporangiophore.Miss Sykes records cases in both Tinesipteris and Psilotnin 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 " sporangiophore" for 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