1896-97-] THE GAMETOPHYTE OF BOTRYCHIUM VIRGINIANUM. 287 



formed in the usual vv^ay, is early lost, and the embryo grows to a 

 relatively large size before the organs make their appearance. The root 

 and shoot originate from the upper part of the embryo ; and it may per- 

 haps be inferred that, like those of Isoetes echinospora, they are derived 

 from the upper octants. The foot is formed from the whole of the lower 

 region of the embryo. The cotyledon is apparently derived secondarily 

 from the shoot meristem. 



(8). The root, the stem, and the cotyledon grow by the segmentation 

 of a single apical cell, as in the adult plant. The root develops more 

 rapidly than the other organs; and the second or third root may make its 

 appearance before the cotyledon unfolds. The latter is green and cap- 

 able of assimilation, as in Ophioglossum pedunculosuvi. 



(9). The root-system of the young sporophyte is soon occupied by a 

 symbiotic fungus, which differs in the size of its filaments and in several 

 other respects, from that found in the gametophyte. 



(10). Evidence of apogamy has been found in the form of prothallial 

 tracheides. 



(11). One example of polyembryony was observed. 



(12). The sporophyte remains for a long time attached to the gameto- 

 phyte. It is an open question whether this is a primitive characteristic, 

 or merely an adaptation. The fact that the young sporophyte of the 

 much less robust B. Lunaria, according to Hofmeister's account remains 

 for a very short period attached to its gametophyte, would seem to 

 justify the latter assumption. 



IX. 



In coming to any conclusions as to the bearing of this research on the 

 phylogenetic position of the Ophioglossacecs, due weight should be given 

 to the fact that the present species is the only one which has been some- 

 what fully investigated ; and the results of recent observations on the 

 Marattiacece, Lycopodiacecs, and Equisetacece show that a very consider- 

 able variety of development may exist even within the same natural 

 group. Moreover the saprophytic habit of the gametophyte of B. vir- 

 ginianum has in all probability more or less profoundly modified its 

 structure. 



It will be convenient to consider first the position of B. virgijiianuni 

 in regard to the other representatives of the OphioglossacecB which have 

 been studied. Its prothallus resembles very closely that of B. Lunaria, 

 and shows indications of being only a more specialized type. That this 



