284 MOSSES AND FERNS chap. 



cotyledon, one in an almost opposite -direction to the primary- 

 root, and a very much shorter one to the young stem apex, 

 which lies close to the base of the cotyledon. ' The outer layer 

 of cells of the cotyledon forms a pretty clearly defined epidermis 

 separated from the axial procambium strand by several layers 

 of young ground-tissue cells. 



The apex of the young stem is occupied in some cases, at 

 least, by a single apical cell, vi^hich probably is to be traced back 

 directly to one of the original octants of the embryo. Whether 

 this is always the case in the youngest stages cannot be de- 

 termined until further investigations are made. Farmer (3) 

 was unable to make out a single initial in Angiopteris, which 

 otherwise agrees closely with Marattia. Dancea, according to 

 Brebner ( i ) , shows a single initial cell at the stem-apex, as well 

 as that of the primary root. 



The study of the root was confined mainly to the older 

 embryos, and although some variation is noticed, it is pretty 

 certain that there is a single apical cell, not unlike that found 

 in the Ophioglossacese. Whether this can be traced back to 

 one of the primary hypobasal octants, it is impossible now to 

 say; but Farmer's statement that in Angiopteris there is at first 

 a three-sided apical cell would point to this. Unfortunately 

 my own preparations of Marattia were too incomplete to decide 

 this point in the latter. In the older root the form of the apical 

 cell was usually a four-sided prism, from all of whose faces 

 segments were cut off, although sometimes an approach to the 

 triangular form found in the Ophioglossacese was observed. 



The foot is much less prominent than in Botrychium, and 

 in this respect the Marattiacese are. more like Ophioglossum 

 (Mettenius (2), PI. xxx). In Marattia all the superficial cells 

 of the central region of the embryo become enlarged and afct as 

 absorbent cells for the nourishment of the growing embryo. 



As the embryo grows, the surrounding prothallial tissue 

 divides rapidly, and a massive calyptra is formed which com- 

 pletely encloses the young sporophyte for a long time. Owing 

 to the position of the cotyledon and stem, which grow up 

 vertically through the prothallium, a conspicuous elevation is 

 formed upon its upper side, through which the cotyledon finally 

 breaks. A similar elevation is formed by the calyptra upon 

 the lower side, through which the root finally penetrates, but not 

 until after the cotyledon has nearly reached its full development. 



