402 SPHENOPHYLLALES. A. SPHENOPHYLLEAE 



and position of the sporangiophores, as well as in the number of the 

 sporangia borne by each of them. These differences offer curious analogies 

 to those of floral construction in Angiosperms : but the latitude of 

 variation here shown is such as would in Angiospermic flowers form the 

 basis of much wider distinctions than those of species, or even of genera. 

 It is not improbable that upon this basis the genus will ultimately be 

 broken up, as detailed knowledge of it increases : meanwhile the following 

 types of disposition of the sporangia have been described. 



The simplest is that seen in S. trichomatosum, Stur, from the Middle 

 Coal Measures, where the sporangia appear solitary near to the axils of 



the subtending bracts, which were here of very 

 narrow form. It is an open question whether 

 the single sporangium was here really sessile, 

 or was borne upon a vascular stalk, as in other 

 species, but in this case exceptionally short. The 

 evidence derived from impressions does not suffice 

 Fi( to decide this point (Fig. 218). From the guarded 



statements of Zeiller, 1 it appears probable that a 



Sphenophyll-um tnclwinatosiini, 



Stur. Diagrammatic figure of the similar disposition of the sporangia is found also 



arrangement of the sporangia. 



(After Kidston.) in S. aiigiistifolium and tenerrimum^ and it may 



be noted that these are all small species with 



narrow leaves. In the well-known S. cuneifolium, Stern (S. Dawsoni, 

 Will, and Scott), each sporangium, single as in the foregoing species, is 

 borne upon an elongated pedicel the sporangiophore. The sporangio- 

 phores in this case are, as a rule, twice as many as the bracts of the 

 subtending whorl: each is traversed by a vascular strand which terminates 

 at the base of the sporangium. The sporangiophores are inserted close to 

 the base of the leaf-verticil, which is here webbed into a wide cup : and 

 to this the pedicels may be adherent for varying distances upwards (Fig. 

 219). The vascular supply of the sporangiophores is derived by branching 

 from that <>/ the subtending bract, of which they thus seem to be 

 appendages. In the regular cases the foliar strand on entering the verticil 

 divides into three, the single lower branch supplies the bract, while the 

 other two enter the two sporangiophores. 2 A further complication is seen 

 in S. Romeri, Solms Laubach, for in this cone two sporangia are borne 

 on each sporangiophore, hanging down from its peltate distal end. The- 

 sporangiophores are disposed in three concentric verticils on each whorl of 

 bracts, and are attached by short stalks traversed by a vascular strand, 

 which branches to supply the two sporangia (Fig. 220). The analogy with 

 the sporangiophore of the Equisetales is more obvious here than in the 

 previous cases, where only a single sporangium is borne on each. But it 

 appears still more plainly in ,V. nia/i/s, Brongn., from the Middle Coal 

 Measures, but as yet known only from impressions. This species is 



</. d. Sphenophyllum, pp. 31, 32. 

 2 For details, see Scott, S/m/i,'*, p. 93, etc. 



