VII PTERIDOPHYTA—FILICWE^—OPHIOGLOSSACEM 249 



mined positively. Probably, as in Botrychium, the outer cell is 

 next divided by a vertical wall, perpendicular to the broad 

 faces of the segment, into two cells, in which divisions then 

 take place in both transverse and longitudinal direction without 

 strict regularity. 



The stem in O. pendulum is mostly made up of thin-walled 

 parenchyma, and the vascular bundles are much less developed 

 than is the case in the underground stem of 0. vulgatum or 

 Botrychium. The bundles are of the collateral form, i. e., the 

 inner side is occupied by the xylem, the outer by the phloem, 



00 



Fig. i34.~'Ophu)glossum pendulum. A, Longitudinal section of stem apex, X6o; B, 

 the central part of the same section, Xi8o; D, longitudinal section of very young 

 sporangiophore, Xi8o; E, cross-section of young sporangiophore, X6o. 



and there is no evident bundle-sheath developed. The bundles 

 form a very irregular wide-meshed cylinder, not differing essen- 

 tially from that in O. vulgatu/L 



Van Tieghem (7) states that in Ophioglossum vulgatum 

 each vascular strand is completely invested with a distinct 

 endodermis and pericycle; but Bower (16) found the endoder- 

 mis very poorly developed in the species studied by him, 

 especially 0. Bergianum, a small and simple species. The stem 

 of this form shows in transverse section two strands which may 



