212 ORIGIN AND RELATIONSHIPS OF THE EUSPORANGIATAE 



The most marked difference in the character of the reproductive organs is the 

 spermatozoid. The spermatozoids in the Eusporangiates, especially in Ophto- 

 glossum, are very large and possess numerous cilia, while in Anthoceros they are 

 minute and have but two cilia, like the other Bryophytes. This is perhaps the strong- 

 est reason for assuming that there is not a direct connection between the Anthoce- 

 rotes and the Ophioglossaceae; but both gametophyte and sporophyte have so many 

 points in common that it may be pretty safely assumed that the progenitors of the 

 Ophioglossaceae were not very different, in appearance at least, from the living An- 

 thoceros. Whether the differences in the spermatozoid are secondary remains to be 

 seen, but in view of the extraordinary constancy of the form of the spermatozoids 

 in all of the main groups of the Archegoniates, one would certainly expect that large 

 multiciliate spermatozoids would be found in the ancestors of the Eusporangiates, 

 supposing these should ever be discovered. 



There is no question that the subterranean prothallium of the Ophioglossaceae 

 is a secondary condition, derived from some green gametophyte, probably very much 

 like that of the Marattiaceae. Not only has the chlorophyll been lost, but in Ophio- 

 glossum and Helminthostachys the dorsiventral form of the gametophyte has been 

 replaced by a radially symmetrical thallus. While this may be partially explained 

 as the result of the absence of light, it must be remembered that the equally sub- 

 terranean prothallium of Botrychium is dorsiventral, although the reproductive 

 organs are borne upon the dorsal surface and not upon the ventral one, as they are 

 in most ferns. Whether this position of the reproductive organs is the result of the 

 conditions of growth or whether it indicates that the green gametophyte from which 

 this saprophytic underground form is descended also bore the reproductive organs 

 dorsally, as most liverworts do, can only be conjectured. In the Marattiaceae 

 antheridia are not uncommon upon the doisal surface, and according to Jonkmann 

 archegonia also may occur dorsally. Whether this is normal or is the result of unusual 

 Hght conditions was apparently not investigated. The formation of archegonia in the 

 ordinary ferns may be induced upon the dorsal side of the prothallium, provided 

 it is illuminated from below. If the illumination is equal on both sides, archegonia 

 will develop both on the ventral and dorsal surface. 



Of the investigated species of Ophioglossum, 0. moluccanum and the nearly 

 related and perhaps identical O. pendunculosum probably represent the most primi- 

 tive type. In these species there may be a feeble development of chlorophyll in the 

 gametophyte under certain conditions and the saprophytic habit is much less pro- 

 nounced than it is in the other species oi Ophioglossum and Botrychium. 



The development of an endotropic mycorrhiza in the prothallium of the 

 Marattiaceae is an interesting suggestion as to the probable beginning of the sapro- 

 phytic habit which characterizes the gametophyte of the Ophioglossaceae. There 

 seems to be good reason to suppose that the peculiar type of symbiosis, which is 

 developed so highly in the Ophioglossaceae, began by the development of a fungus 

 associate in some green gametophyte like that of the Marattiaceae. 



The reproductive organs of the Ophioglossaceae and Marattiaceae are very 

 similar indeed. It is probable that the short-necked archegonium found in the 

 Marattiaceae and in Ophioglossum is more primitive than the long-necked arche- 

 gonium of Botrychium or Helminthostachys. This conclusion is based upon the 

 assumption that the four-necked archegonium of the ferns is a development of the 

 four terminal cells in the neck of the Bryophyte archegonium, Anthoceros most 

 nearly approaching this hypothetical ancestral type. This being the case, the forms 

 with the shortest neck would most nearly resemble this assumed ancestral type. 



