Part III. THE ORIGIN AND RELATIONSHIPS OF 

 THE EUSPORANGIATE. 



The eusporangiate ferns as they now exist represent but a few isolated fragments 

 of what in earlier geologic time was presumably a very much larger and more con- 

 nected group. As the geological history of these forms is very far from clear (this 

 being especially true of the Ophioglossaceae), we are, perforce, dependent mainly 

 upon a comparative study of the few existing types for information concerning their 

 relationships. In the foregoing pages an endeavor has been made to trace the de- 

 velopment of these forms, both in their gametophytic and early sporophytic stages, 

 and the result of these studies has been to confirm the belief that a real genetic- 

 relationship exists between the Marattiaceae and the Ophioglossaceae. 



While the three genera of the Ophioglossaceae differ in certain particulars from 

 each other, there is no question as to their being comparatively closely related, and 

 the same is true of the different genera of the Marattiaceae, although perhaps the 

 differences here are somewhat greater than in the Ophioglossaceae. 



It has been assumed in these studies that the sporophyte of the ferns is the 

 result of a progressive specialization of the sporogonium of some form allied to the 

 Bryophytes, though it is highly improbable that any of the existing Bryophytes are 

 directly related to this progenitor of the primitive ferns. No attempt will be made 

 here to discuss the reasons for accepting the "antithetic" theory of the alternation 

 of generations, rather than the homologous theory. These reasons have been set 

 forth at length elsewhere. 



It is hopeless to expect that any satisfactory fossil traces will be found of these 

 predecessors of the true ferns. The fern type is exceedingly ancient, but it must 

 have been preceded by simpler forms connecting it with some bryophytic type. 

 These forms, as well as the earlier true Pteridophytes, were almost certainly plants of 

 small size and delicate texture, probably not very unlike some of the small and 

 delicate species of Ophioglossum. Such plants, composed entirely of soft, perish- 

 able tissues, could hardly be expected to leave recognizable fossil traces, and their 

 absence from the ancient Paleozoic rocks is not to be wondered at. 



There still exist, however, among the Bryophytes, certain forms which, if they 

 are not directly related to the eusporangiate ferns, nevertheless show many striking 

 similarities in structure, which help to explain at least what may very well have been 

 the character of the liverwort-like ancestors from which the ferns are descended. 

 Among the living Bryophytes, as is well known, an interesting series of types may be 

 traced, showing the gradual increase in the importance of the neutral generation — 

 the sporophyte — starting as little more than a mass of spores, finally by a progressive 

 sterilization of what was originally sporogenous tissue, and an accompanying special- 

 ization of the sterile tissues thus formed, attaining a condition of almost complete 

 independence. The importance of this process of sterilization of potentially sporo- 

 genous tissue, has been especially clearly expounded in the works of Professor Bower. 



In two classes, the true mosses or Musci and the horned liverworts or Antho- 

 cerotes, the sporophyte continues its growth for several months and develops an 

 elaborate system of green, assimilative tissue, quite comparable to that found m 

 the vascular plants. The spore-producing function is correspondingly subordinated 

 and the spore formation is delayed until a late period in the life of the sporophyte. 

 14 2oy 



