OF CALAMITEAN STROBILUS. 257 



Fig. 8 represents portions of two of the vessels from 

 fig. 7, e, more highly magnified, and exhibiting the reti- 

 culated character which has hitherto proved so distinctive 

 of Calamopitus. They have a variable diameter of from 

 Fou to tAu of an inch. 



The outlines of some of the sporangia are very distinct 

 in fig. 7_, the sporangium-walls (/, /') being more continuous 

 and regular than usual, whilst the spores (i), indicated in 

 the drawing by the dark mottled surfaces, are packed very 

 closely round the main axis. 



Fig. 9 is a transverse section of one of the sporangio- 

 phores from the unfigured part of the section of which 

 fig. 5 is the central portion. Its dorsal surface, h, is 

 rounded; but its opposite or inner margin projects as a 

 strongly defined keel (^'), owing to two deep lateral exca- 

 vations, which gives this part of the organism a compressed 

 form. It chiefly consists of densely aggregated elongated 

 cells, or prosenchyma, with vague traces of vascular tissue ; 

 but in all the longitudinal sections, its structure is so 

 dense and black that the details are not easily made out. 

 The greatest diameter of this sporangiophore is about y^ 

 of an inch, and its lesser or transverse diameter about yg-^ 

 of an inch. 



The numerous spores are enclosed in sporangia, the 

 structure of the investing membranes of which appear to 

 be almost identical with those of the Calamitean strobili 

 described by Mr. Binney and Mr. Carruthers. These 

 sporangium-walls are cellular, the oblong cells being 

 arranged vertically to the two surfaces of the membrane, 

 which is about -g-Jpo of an inch in thickness, whilst the in- 

 dividual cells have a diameter of from t^xi-o to 20^00 of an 

 inch, the latter being the more usual dimensions. Exter- 

 nally, the ends of the cells are generally plane (fig. 10, /'), 

 whilst their inner extremities (/) are somewhat convex and 

 turgid ; but these difierences are not constant. In some 



SER. III. VOL. IV. s 



