464 OPHIOGLOSSALES 



regions, those in the former being ultimately forked, giving a " Neuropteris " 

 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 

 lateral pinna which has taken a median position. 



Lastly, the relation of the vascular system to the sporangia deserves 

 notice. In Ophioglossum 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 

 doubtless efficient in the case of deeply sunk sporangia (compare Fig. 250) 

 But in Botrychium and Helminthostachys the ultimate strands terminal 

 immediately below the base of each sporangium. The condition seen ii 

 Ophioglossum does not appear to accord well with a theory of sporangia 

 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 b) 

 formation of a leaf-gap at the exit of each leaf-trace : the latter is typicalb 

 a single strand: as it passes upwards it branches, with prevalent bifurcation ii 

 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, s< 

 that it is now possible to give some approach to a comparative account 

 of the embryology of the family. 1 



1 The account here given is based upon the works of Hofmeister, Higher Cryptogamia, 

 1862 ; Mettenius, Filices Horti Lipsiensis, 1856 ; Campbell, Mosses and Ferns, 1895 am 



