XIX] COMPARISON 91 



The gametophyte does not greatly help in the morphological comparison 

 of the Ophioglossaceae. Nevertheless there are some significant features 

 which though slight in themselves acquire additional weight because they 

 point to the same conclusions as follow from the study of the sporophyte. 

 Botrychium stands alone in having a flattened form of its prothallus: and 

 though its sexual organs are borne upon the upper surface this is not 

 unknown in the flattened green prothalli of Ferns, to which it is the nearest 

 approach seen in the family. The sexual organs themselves are highly 

 standardised for the family: but Campbell specially remarks upon the size 

 of the antheridia of O. pendnluni, and the number of its spermatocytes, 

 "perhaps more than in any Pteridophyte." This runs parallel with the 

 sporangia of the same species, which show a specially large spore-output. 

 On the other hand, the archegonia of OpJiioglossiiiii are more deeply sunk 

 than in the other genera, and this appears in the most pronounced form 

 in O. pendulum. In fact the genera may be seriated roughly by their 

 gametophytic characters with results corresponding to those based upon 

 their anatomy, their sporangia, and their external form. Lastly, their 

 embryology leads to a like result. Botrychium obliqutun and Helminthostachys 

 have endoscopic orientation of the embryo with a suspensor, and their 

 embryos are subject in consequence to awkward curvatures during develop- 

 ment. The sections \Eu-Botrychiuni and \Osmundopteris on the other hand 

 have no suspensor, and their orientation is exoscopic, while their embryos 

 have no curvature: and this is so for all the species of Ophioglossum. When 

 finally we see in O. violuccanum and pendulum an extreme delay in the 

 development of the stem-apex, accompanied by those peculiarities described 

 in detail by Campbell, the cumulative conclusion seems justified that these 

 illustrate not a primitive state, but probably the most advanced and 

 specialised embryological condition that the family has produced. 



Phyletic Arrangement of the Ophioglossaceae. 



It is concluded then that the Ophioglossaceae are a family of primitive 

 Ferns, allied especially to the Coenopteridaceae, but with some degree of 

 affinity also with the Osmundaceae and the Marattiaceae. Within the 

 family Botrychmm and Helminthostachys appear to be relatively primitive 

 genera, and Ophioglossum more highly specialised. This follows from the 

 details of external form, venation, anatomy, and the characters of the 

 gametophyte, sexual organs, and embryogeny above detailed. But it is 

 difficult to assign to either of these more primitive genera the prior place. 



Helminthostachys is represented only by a single species, of the limited 

 Indo-Malayan region, a fact which may be held to indicate antiquity. The 

 form and venation of the leaf, the stelar structure, and the undivided leaf- 



