296 MOSSES AND FERNS chap. 



existing, which probably are merely remnants of groups once 

 much more abundant. This is certainly true of the Maratti- 

 aceae, and presumably is the case with the Ophioglossaceae and 

 Isoetaceae as well. In the former order this is amply proven 

 by the geological record ; but in the others the fossil forms 

 allied to them are very uncertain, and as yet poorly understood. 

 In the Ophioglossaceae the series from OpJiioglossuin through the 

 simpler species of Botrychium to the higher ones, such as 

 B. Virginianunt, is complete and unmistakable, but when 

 points of connection between these and other forms are sought, 

 the matter is not so simple. 



Our still very incomplete knowledge of the gametophyte 

 of the Ophioglossaceae makes the comparison doubly difficult. 

 From the development of chlorophyll in the germinating spore 

 of B. Virginianum, as well as from analogy with other Ferns, it 

 seems probable at any rate that the subterranean chlorophylless 

 prothallium is a secondary formation, but this cannot be asserted 

 positively until the development is much better known than at 

 present, and its relation to the green prothallium of the Maratti- 

 acese and the thallus of the Hepaticae must remain in doubt. 

 The structure of the sexual organs and development of the 

 embryo point to a not very remote connection with the former 

 order, and in some respects also to the Anthoceroteae. 



Ophioglossuvi beyond question shows the simplest type of 

 sporangium of any of the Pteridophytes, and may be directly 

 compared to a form like Anthoceros. In both cases the arche- 

 sporium is hypodermal in origin, and is formed without any 

 elevation of the tissue to form separate sporangia. In Antho- 

 ceros, alternating with the sporogenous cells, are sterile cells 

 which divide the archesporium into irregular chambers containing 

 the spores. A direct comparison may be drawn between this 

 and the origin of the archesporium in OpJiioglossum, except that 

 in the latter the archesporium seems to be discontinuous, 

 and from the first separated into parts corresponding to the 

 separate sporangia. In some species of Ophioglossuni, too, the 

 epidermis above the sporangium has stomata as in Anthoceros. 

 A comparison of these remarkable points of similarity in the 

 structure of the sporophyll of Ophioglossuvi and the sporogonium 

 of Anthoceros, together with the very simple tissues of the 

 former, led the writer ^ to express the belief that OpJiioglossuin, 



^ Bot. Gazette, Jan. 1890. 



