464 OPHIOGLOSSALES 
regions, those in the former being ultimately forked, giving a ‘‘ europteris” 
venation, as in Botrychium. All these arrangements are clearly variants 
upon one plan, of which the essential point is that the vascular supply 
of the spike is of marginal origin, right and left from that of the whole 
leaf. It was upon this that Roeper based the anatomical support for 
his theory of the spike as a result of fusion of lateral pinnae. The facts 
would accord, it is true, with Roeper’s theory; but it is to be borne in mind 
that a marginal origin of vascular strands from the main system is much 
more usual in leaves than any antero-posterior branching. On the other 
hand, the origin of the vascular supply of the spike from both sides of 
the foliar system gives no support to the theory that it is essentially a 
lateral pinna which has taken a median position. 
Lastly, the relation of the vascular system to the sporangia deserves 
notice. In Ofhdoglossum lateral branches from the anastomosing strands 
of the spike pass between the sporangia, traversing the septum and expanding 
toward the periphery into a tuft of tracheides, an arrangement which is 
doubtless efficient in the case of deeply sunk sporangia (compare Fig. 250). 
But in Botrychium and Helminthostachys the ultimate strands terminate 
immediately below the base of each sporangium. The condition seen in 
Ophioglossum does not appear to accord well with a theory of sporangial 
fusion: it points rather to an upward process of progressive septation. 
Summarising the results of this anatomical examination of the shoot 
in the Ophioglossales, the facts are consistent with the origin of the axial 
system from a protostelic state, with amplification of the stele, followed by 
formation of a leaf-gap at the exit of each leaf-trace: the latter is typically 
a single strand: as it passes upwards it branches, with prevalent bifurcation in 
Botrychium and Helminthostachys, but not in Ophioglossum: these facts are 
consistent with an origin of the leaf from a simpler source by enlargement 
and branching. The vascular supply to the fertile spike originates from 
the lateral margins of the foliar system, and with this the simpler states 
of O. palmatum coincide, though not the more complex. The bearing of 
these facts, as indicating the probable origin and relationships of the 
Ophioglossales, will be discussed later. 
EMBRYOLOGY. 
Until recently the prothallus and the development of the embryo in 
the Ophioglossales were very imperfectly known, though observations 
upon them date back to the writings of Hofmeister and of Mettenius. 
But during the last ten years the prothalli and embryos have been dis- 
covered in a number of cases where they were previously unknown, so 
that it is now possible to give some approach to a comparative account 
of the embryology of the family.? 
1The account here given is based upon the works of Hofmeister, Higher Cryptogamia, 
1862; Mettenius, Filices Horti Lipsiensis, 1856; Campbell, Mosses and Ferns, 1895 and 
