268 



PLANT MORPHOLOGY 



gives rise to an upright cylindrical branch bearing sex organs. As in 

 Bolnjchium, the antheridia appear before the archegonia. 



The antheridium of the Ophioglossales is large and sunken (Fig. 225 A, 

 B). It develops as in the lower pteridophytes, the spermatogenous tissue 



B D 



Fig. 224. Prothallia of Ophioglossales. A, prothallium of Botrychium virginianum with 

 dorsal ridge bearing antheridia, X 16; 5, cross section of same, showing antheridia on ridge, 

 archegonia on the sides, and fungal zone below, X17; C and D. Ophioglossum vulgatiim; 

 C, entire prothallium, about X2; £), one-half of a prothallium with antheridia and arche- 

 gonia on surface and, to left, a young sporophyte with first root, X30. (A and B, after 

 Jeffrey; C and D, after Bruchmann.) 



arising from the inner segment resulting from a periclinal division of the 

 superficial initial. In Ophioglossum the wall remains one-layered, but in 

 the two other genera it becomes two-layered. The sperms are numerous, 

 large, coiled, and multiciliate (Fig. 225C). The archegonium initial is 

 also superficial and divides periclinally, the outer cell forming the neck 

 and the inner one giving rise to the central cell and basal cell (Fig. 

 225D-G). A basal cell is not present, however, in some species of 

 Botrychium. The axial row, derived from the central cell, consists of a 



