INTRODUCTION. 



It is pretty well agreed among botanists that most of the seed plants, perhaps 

 all of them, are descendants of some fern-like Paleozoic ancestors. The geological 

 record is remarkably perfect in many respects, and our knowledge of many of these 

 Paleozoic fossils is extraordinarily complete. Among the most important con- 

 tributions made of late years to our knowledge of these Paleozoic fossils is the fact 

 that many of these Paleozoic "ferns" were really seed-bearing plants intermediate 

 in character between the true ferns and the more highly developed flowering plants. 



At best the fossil record is very incomplete in regard to many extremely impor- 

 tant structural details, and therefore it is especially necessary that these points 

 should be thoroughly studied in such of the existing ferns as, for any reason, seem 

 to be at all closely related to the ancient Paleozoic types. 



The name Eusporangiatse was proposed by Goebel to include the two very 

 peculiar families of fern-like plants, the Marattiaceas and Ophioglossaceae, which 

 differ in several important respects from the much more numerous and specialized 

 Leptosporangiatae, the predominant ferns of the present day. The Eusporangiatse 

 comprise lOO or more species of widely distributed ferns, of which the Marattiaceae 

 are mainly tropical in their distribution, while the Ophioglossaceae include a good 

 many species of temperate regions as well. The Eusporangiatae are distinguished 

 primarily by the character of the sporangium, which is always much more massive 

 than in the typical ferns, the Leptosporangiatae. In the latter, the sporangium can 

 almost always be traced back to a single mother cell which usually arises from the 

 surface of the leaf, while in the Eusporangiatae the sporangium is already multi- 

 cellular when it is first recognizable. 



The Marattiaceae are in general appearance much like the typical ferns, and 

 there is no question of their relationship to the Leptosporangiatae. The resem- 

 blances are less obvious in the case of the Ophioglossaceae, and some students of 

 the ferns have expressed the opinion that the Ophioglossaceae should be separated 

 entirely from the ferns and placed in a distinct class. (See Bower 9.) A careful 

 comparative study, however, of the two families included in the Eusporangiatae shows 

 so many close correspondences in structure, both of the sporophyte and gameto- 

 phyte, that their association together is amply justified. 



The Marattiaceae are known to be very ancient forms, unmistakable members 

 of this family occurring abundantly in Paleozoic formations. The Ophioglossaceae, 

 on the other hand, are very unsatisfactorily represented in a fossil condition, and 

 fdr this reason doubt has been thrown on their antiquity, although their structures 

 show strong evidences of an extremely primitive character. Certain of the oldest- 

 known fossil ferns, the Botryopterideae, may possibly prove to be related to the 

 Ophioglossaceae, but the evidence at present is not entirely conclusive. 



In spite of the unsatisfactory nature of the geological evidence, I am neverthe- 

 less strongly inclined to believe that the Ophioglossaceae, on the whole, represent 

 the most ancient type among the living ferns, this conclusion being based upon a 

 very careful study of the structure of both gametophyte and sporophyte. 



There are many practical difficulties in the way of studying these interesting 

 ferns, and these difficulties undoubtedly account for the comparatively small number 

 of researches that have been made upon their development. A few species, like 

 Ophioglossum vulgatum and several species of Botrychium, are widespread in their 



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