CONCLUSION. 



While the more specialized Marattiaceae, like Marattia and Angiopteris, 

 apparently diflFer very much from the Ophioglossaceae, it appears from a study of 

 the development of these forms, as well as that of the simpler and presumably more 

 primitive genera Dancea and Kaulfussia, that the most conspicuous differences are 

 of secondary rather than of primary importance, and the conclusion is justified that 

 the two families of the Eusporangiatae really arose from the same primitive stock. 

 Of the Ophioglossaceae, H elminthostachys is undoubtedly the form which, on the 

 whole, comes nearest to the Marattiaceae, although Ophioglossum is more like them 

 in the character of the reproductive organs and in the vascular skeleton of the 

 sporophyte. Ophioglossum also recalls Kaulfussia in the form and venation of 

 its leaves. 



While the green gametophyte in the Marattiaceae is undoubtedly a more 

 primitive structure than the saprophytic prothallium of the Ophioglossaceae, the 

 sporophyte of the latter is certainly a more primitive one than that of the Marat- 

 tiaceae. The monophyllous condition, the early development of the sporangia, and 

 the fact that the whole of the sporangiophore is spore-bearing, all point to this. 



The way in which the sporophyll of the Marattiaceae has been derived from a 

 type like that of the Ophioglossaceae is not clear, and it is by no means certain that 

 all of the Marattiaceae have been developed in the same way. The occurrence of 

 fossil forms with sporangia of the marattiaceous type grouped together — much like 

 the sporangia of Botrychium or Osmunda — suggests that such a condition might have 

 been preliminary to the separation of the sporangia by the development of sterile 

 green tissue in the sporangiophore, such as sometimes occurs in H elminthostachys. 

 The converse is not tenable unless we accept the view that the sterile leaf is an 

 older structure than the sporangiophore, a view which we believe is not warranted 

 by the facts. It has been suggested in a previous chapter that the sporophyll of the 

 Marattiaceae might be accounted for by a theory of concrescence of the sporangiophore 

 and sterile lamina in the Ophioglossaceae. Ophioglossum palmatum, with the two 

 series of small sporangiophores and broad leaf lamina, is the form which comes 

 nearest to such a condition. A very serious objection to this view was mentioned, 

 however — the fact that the sporangiophore is an adaxial structure, whereas the 

 synangia of the Marattiaceae are always abaxial in their position. 



Comparing the eusporangiate ferns with the leptosporangiate, it is generally 

 conceded that the Osmundaceae are the ferns which most closely approach the 

 Eusporangiatae. The Osmundaceae show points of resemblance to both the Ophio- 

 glossaceae and Marattiaceae, this being true both of the vegetative tissues and the 

 sporangia. In Osmunda the arrangement of the sporangia suggests Botrychium, 

 while in Todea the sporangia are borne upon the backs of the leaves, much as they 

 are in the Marattiaceae. Bower has suggested that the Gleicheniaceae, which are, 

 however^ certainly allied to the Osmundaceae also, show certain suggestions of a 

 marattiaceous affinity, especially in the arrangement of the sporangia. 



We may then briefly summarize our conclusion as follows: From some form, 

 allied to the simpler existing species of Ophioglossum, the whole fern series is 

 descended. In this whole series the leaf is the predominant organ, the stem at first 

 being quite subordinate in importance. This ancestral fern was monophyllous and 

 the leaf at first was a sporophyll, perhaps without any definite sterile segment. 



217 



