126 TRANSACTIONS. NATURAL HISTORY SOCIETY OF GLASGOW. 



belongs to the sporangium of the first whorl, that nearest to the 

 axis, or to that of the second or third whorl, and consequently 

 more distant from the axis. 



Each succeeding circle of sporangia was raised slightly above 

 that lying inside of it or nearer the axis, on account of the 

 upward slope of the bracts. Thus the second circle of sporangia 

 holds a higher level than the first, and the third a higher level 

 than the second circle. Hence in transverse sections of the cones 

 the sporangia are cut through at different levels. 



At the apex of the sporangium, where the sporangiophore 

 merges into it, the cells are larger with thicker walls, and Zeiller 

 points out that these have very much the structure and appear- 

 ance of the cells forming the annulus on the sporangia of ferns. 1 

 It is probably through the agency of this somewhat oblique cap 

 of larger cells that the sporangium was split at maturity. 



In the specimens examined by Williamson and Scott the 

 spores are all of one kind. Their outer surface is ornamented 

 with spines connected by ridges, which give them a characteristic 

 reticulate appearance. No specimens yet discovered give any 

 support to the view that Sphenophyllum was heterosporous. 2 



The free portions of the bracts, into each of which runs a small 

 vascular bundle, extend upwards past several internodes, hence 

 in transverse sections of the cone it is usually surrounded by 

 several circles of bracts, sometimes as many as six, cut at 

 different levels. It would appear from the position of the 

 various members of these bracts that the whorles alternate in the 



1 Zeiller, Constitution d. Vappartil fruct. Sphenophyllum, p. 17, woodcut 

 F. See also Williamson, Phil. Trans,, Vol. CLXXXIL, Mem. XVIII. , 

 PI. XXVIII., fig. 16, 1891; and Williamson and Scott, Phil. Trans., Vol. 

 CLXXXV., p. 939, 1895. 



2 Renault has figured a specimen which he refers to Sphenophyllum, in 

 which is described macrosporangia and microsporangia, the latter attached 

 directly to the limb of the bract. The specimen is a good deal broken up, 

 and does not appear to give any support to the opinion that Sphenophyllum 

 was heterosporous. Renault, Ann. de Science Nat., 6 e Ser. Bot., Vol. IV., 

 pp. 303-304, PI. IX., figs. 9, 10, 11, 1876. (" Nouvelhs rech. sur la struc- 

 ture des Sphenophyllum et sur leur affinities boianiques.") Renault, Cours. 

 d. boian.foss.,Yo\., II., pp. 102-103, PI. XV., figs. 7-8; PI. XVI. , fig. 3, 1882. 

 Renault, Flore foss. Etudes sur le terr. houil. de Ccmentry, pp. 481-482, 1S90. 



