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 



FIG. 247. 



Ophioglossmn vulgatmit. ,4= par), of a 

 longitudinal section including the apex of the 

 fertile spike, and traversing the sporangiogenic 

 band longitudinally. B = tangential section, 

 following the sporangiogenic band, and 

 showing the regularity of its cells. C = lateral 

 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. 



FIG. 248. 



Ophioglossum (pphioderma) pendulum, L. A = 

 transverse section of spike showing sporangiogenic 

 band. B = longitudinal section following it, and 

 showing it already differentiated, with sporogenous 

 groups. C= tangential section of a spike of like 

 age, also showing two sporogenous groups. 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 



2 F 



