SPORE-PRODUCING MEMBERS 449 
fertile tissue, while the outer tissue begins to constitute the protective 
wall. But the whole of the cells composing these sporogenous groups do 
not become matured into spores; for a peripheral part of each group takes 
the character of tapetum, and becomes disorganised as the development 
Fic. 247. Fic. 248. 
Ophioglossum vulgatum. A=part of a Ophioglossum (Ophioderma) pendulum, L. A= 
longitudinal section including the apex of the transverse section of spike showing sporangiogenic 
fertile spike, and traversing the sporangiogenic band. S#=longitudinal section following it, and 
‘ band longitudinally. B=tangential section, showing it already differentiated, with sporogenous 
following the sporangiogenic band, and groups. C=tangential section of a spike of like 
showing the regularity of its cells. C=lateral age, also showing two sporogenous groups. X00. 
part of a transverse section of a spike; the 
cells shaded are recognised as the sporangio- 
genic band. D=a similar section showing an 
older state. X 100. 
of the spores proceeds. The outline of the definitive sporogenous group 
which remains is very variable: sometimes it is relatively regular, as 
in Fig. 249 D; but in other cases, which may even occur in the same 
sections as the regular ones, the disposition of the cells is less regular. 
These have probably arisen from parts of the sporangiogenic band which 
2F 
