ORIGIN AND RELATIONSHIPS OF THE EUSPORANGIATAE 213 



The question of the canal cells is a puzzling one. In the Marattiaceae, with the 

 exception of Danxa, two neck canal cells, or at any rate two nuclei, are present and 

 the ventral canal cell is conspicuous. In Dancea, however, the canal cells are very 

 much less perfectly developed, the ventral canal cells especially being exceedingly 

 difficult to demonstrate. In the latter respect Danaa shows a remarkable resem- 

 blance to the Ophioglossaceae, especially to Ophioglossum, where the ventral canal 

 cell is equally difficult to demonstrate. This apparent degeneration of the ventral 

 canal cell is probably secondary, as all of the Bryophytes and the other Pteridophytes 

 have the ventral canal cell conspicuous. 



The antheridium in all of the Marattiaceae is almost exactly like that of Ophio- 

 glossum, while Botrychtum and Helminthostachys differ in having the outer wall of 

 the antheridium more or less completely two-layered. If the antheridium is derived 

 from a type like that of Anthoceros (fig. 192), where the antheridial cavity is covered 

 by a double layer of cells, it would seem that Botrychium and Helminthostachys are 

 more primitive than Ophioglossum or the Marattiaceae in this respect. 



Of the Eusporangiates, there is no question that the type of embryo found in 

 Ophioglossum moluccanum comes the nearest to the assumed ancestral form. This 

 hypothetical pro-fern may be assumed to have developed simply a spore-bearing 

 organ or sporangiophore, perhaps more or less leaf-like, and a root developed from 

 the inner part of the massive foot in the same way that the root actually does develop 

 in the embryo of the Marattiaceae and Ophioglossum moluccanum. Except that the 

 cotyledon of 0. moluccanum is sterile, the young sporophyte in this species is actually 

 like this hypothetical type, viz, it is composed simply of root and leaf. It is probable 

 that the fertile spike of Ophioglossum is not unlike the primitive sporangiophore, 

 and the ancestral form presumably developed such a spike-like sporangiophore from 

 the first, the sterile lamina being a secondary structure arising perhaps from a basal 

 meristem, like that found in the sporophyte of Anthoceros. The early development 

 of the spores in the Ophioglossaceae is a further indication of their primitive nature. 



The monophyllous condition which prevails among the Ophioglossaceae must 

 also be regarded not as a secondary condition but as a primitive one, and a study of 

 the development of the sporophyte lends no support to the theory that we have to 

 do with a reduced strobilus. Of the Marattiaceae, Kaulfussia normally approaches 

 the monophyllous condition more closely than any other genus. The older plants, 

 as a, rule, have only two or three leaves expanded at one time and there may fre- 

 quently be but one. In strong contrast with this is the dense crown of leaves found 

 in Marattia and Angiopteris, although even in these forms the number of leaves is 

 less than it is in the majority of leptosporangiate ferns. The tendency to the mono- 

 phyllous condition is shown in the younger plants of Marattia, developed from the 

 buds on the old leaf bases, where, as a rule, only one leaf is expanded at a time. 



The young sporophyte of 0. moluccanum has no stem. Without exception, for 

 a considerable time at least, the vascular system of the sporophyte is composed 

 exclusively of tissue belonging to the leaves and roots, the stem apex playing no 

 part in the building up of the vascular skeleton. The theory that there is a special 

 stele belonging to the stem, of which the leaf traces and the root traces are sub- 

 sidiary structures, is not borne out by a detailed study of the evolution of the vascular 

 system in either the Marattiaceae or Ophioglossaceae. In all of these that I have 

 examined the vascular system begins as a single strand common to the primary 

 leaf (or cotyledon) and the primary root, and the more complicated vascular system 

 of the older stem for a very considerable period is built up exclusively by additions 

 of new leaf traces or root steles. This condition is permanent in the Ophioglos- 



