222 MOSSES AND FERNS chap. 



The Honiosporons EusporangiatcE 



The two orders, Ophioglossaceae and Marattiaceae, show 

 many evidences of being very ancient forms, and in several 

 respects seem to approach more nearly to the Hepaticae than any 

 other Pteridophytes. While they are different from each other 

 in many respects, still there is sufficient evidence to indicate 

 that they belong to a common stock to warrant placing them 

 near each other in the system. 



The OphioglossacecB 



The gametophyte of the Ophioglossaceae is still very in- 

 completely known, and only in a few forms. Mettenius ^ 

 described the older stages of OpJiioglossum pedunmlosum, and 

 Hofmeister^ similar prothallia of Botrychium lunaria, but they 

 were unable, as later observers have been, to procure the earlier 

 conditions. In both cases the prothallia were subterranean 

 and entirely destitute of chlorophyll. In OpJiioglossum, how- 

 ever, when it reached the surface of the ground, the part exposed 

 to the light became somewhat flattened and green. 



The earliest stages that Mettenius found consisted of a 

 nearly globular tubercle, from which a single conical protuber- 

 ance grew upward, having a branch that in extreme cases 

 reached a length of as much as two inches (Fig. io8). This 

 branch grows by a single apical cell, and may occasionally 

 branch dichotomously, and always grows towards the light. 

 On reaching the surface of the ground the growth is checked 

 and a flattened expansion is produced whose cells contain 

 chlorophyll. The sexual organs are borne almost exclusively 

 upon the subterranean parts of the branch, and in great 

 numbers. On the weaker prothallia antheridia prevail, on the 

 stronger ones archegonia. The structure and development of 

 these correspond closely with those of the other eusporangiate 

 Pteridophytes. The antheridia are completely sunk in the 

 tissue of the prothallium, and the outer wall is composed of 

 two layers of cells (Fig. io8, C). The archegonia have a short 

 neck, which projects but little above the surface. The number 

 of canal cells does not seem to have been determined (Fig. 

 io8, D). 



^ Mettenius (3), p. 119. 2 Hofmeister (i), p. 307. 



