PTERIDOPHYTA 



249 



ing little or no resemblance to the foliage leaves. In Sphenophylhim the 

 bases of the sporophylls were united to form a cup-like sheath, but the 

 tips were free (Fig. 207). The sporangia were borne singly or in pairs on 

 long sporangiophores that arose from the adaxial side of the sporophylls, 



Fig. 206. Reconstruction of the shoot of Sphenophyllum cuneifoUum, one-third natural 

 (From Gilbert M. Smith.) 



size. 



either singly or several together. The sporangia were pendent from the 

 distal end of the sporangiophore, which was often expanded to form a ter- 

 minal disk. The strobilus of Cheirostrohus, a form genus of Carboniferous 

 age, was more complex than that of Sphenophyllum, each sporophyll con- 



