SPORE-PRODUCING MEMBERS 



447 



fertile condition of the leaf is normally the rule in the family ; but that 

 the fertile spike of the Ophioglossaceae behaves like the sporangiophore of 

 the Psilotaceae, or the sporangium of Isoetes or Lycopodium in the matter 

 of its abortion : this is complete in some leaves, while in others a vestigial 

 structure remains to show what has occurred. Further, though their 

 tendency towards a monophyllous .habit may make such a comparison less 

 obvious, the Ophioglossaceae show essentially a " Selago " condition of the 

 shoot, that is, an imperfect differentiation of the vegetative and reproductive 

 functions. Their condition would, in fact, be consistent with a strobiloid 

 origin, modified in further development by enlargement of the appendages, 

 all of which were originally fertile. This matter 

 will be referred to again in connection with the 

 early appearance of the fertile spike in the 

 young seedling plant. 



SPORE-PRODUCING MEMBERS. 



The development of the fertile spike has been 

 traced in Ophioglossum from its first beginnings. 1 

 The leaf itself originates very close to the initial 

 cell of the deeply depressed apex of the axis. 

 The sheathing stipule which envelopes the growing 

 point as well as all the later leaves, is formed 

 early : the spike appears above it in a median 

 position on the adaxial face of the leaf, but near 

 to its base (Fig. 245). The outgrowth is at first ophwgiossum vuigatum. The 



, . lower drawing shows a longitudinal 



bluntly rOUnded, but It SOOn becomes more median section of a young leaf, with 



, . . the spike (sp) arising about half-way 



acute and turned upwards : it consists of several up its adaxial face. The upper 



j f , , .... drawing shows a rather older leaf in 



cells, and of these the uppermost, which is frontal view. x 35 . 

 already the largest (x in the Figs. 246 A, B, c, E), 



undergoes further segmentation with some degree of regularity : its 

 segments go to form the bulk of the free portion of the spike. The 

 form of the initial cell is that of an irregular four-sided pyramid, but in 

 some cases at least its identity is soon lost, and the type of construction 

 passes over to that with four initials (Fig. 246 F, G). As a consequence 

 of further subdivisions, whichever be the type of the initial segmen- 

 tation, the spike comes to be composed of four quarters, separated 

 by walls at right angles, as seen in the transverse section : its form 

 is that of an elongated cone, slightly flattened on its adaxial and 

 abaxial sides. Sections of it, transverse, radial, and tangential, are shown 

 in Figs. 247 A-D : from these it appears that a special band of cells, the 

 sporangiogenic band, runs along the lateral margins of the slightly flattened 



1 The account here given is condensed from the full statement (Studies, ii., pp. 10-27), 

 where the literature is quoted. The development has been worked out for three species : 

 O. rulgatinn, reticu/atu/n, and pendulum. 



FIG. 245. 



