In another type of Sphenophyllum strobilus, recently described by Solms-Laubach, the incurved end of each sporangiophore bore two sporangia. In most respects this species, which has not been found in connection with a vegetative shoot, agrees with Sphenophyllostachys Dawsoni.

In fig. 107, C, which is copied from one of Solms-Laubach’s drawings[891], we have an oblique transverse section of part of a strobilus, including portions of two series of sporangia borne on one verticil of bracts, and at the right-hand edge the section has passed through the sporangia belonging to another whorl of bracts. There were probably three concentric series of sporangia attached to each verticil of bracts, as in the case of fig. 108. The unshaded area, b (fig. 107, C), represents the bracts of two successive sterile whorls in transverse section. The shaded areas are the sporangia, with their sporangiophores, s. The relative position of the sporangia and sporangiophores suggests that each pedicel bore two sporangia at its tip, instead of one, as in the strobilus of Sphenophyllum cuneifolium (Sternb.).

A further variation in the structure of the strobili is illustrated by some specimens of S. trichomatosum Stur, described by Kidston[892], from the Coal-Measures of Barnsley. Each whorl of bracts bears a single series of oval sporangia which appear to be sessile on the basal portion of the whorl. It is possible that delicate sporangiophores may have been present, but in the imperfect examples in Kidston’s collection[893] the sporangia present the appearance of being seated directly on the surface of the bracts. As the specimens do not show any internal structure, it would be unwise to lay too much stress on the apparent absence of the characteristic sporangiophores. In any case, Kidston’s cones afford an illustration of the occurrence of a single series of sporangia in each whorl, instead of the pluriseriate manner of occurrence in some other species.

The statement is occasionally met with that some Sphenophyllum cones possessed two kinds of spores, but we are still in want of satisfactory evidence that this was really the case. Renault has described an imperfect specimen, which he considers points to the heterosporous nature of a Sphenophyllum cone, but Zeiller and Williamson and Scott have expressed doubts as to the correctness of Renault’s conclusions. While admitting the possibility of undoubted heterosporous strobili being discovered, we are not in a position to refer to Sphenophyllum as having borne strobili containing two kinds of spores[894].

SPHENOPHYLLUM EMARGINATUM.

[The following are some of the specimens in the Williamson Cabinet which illustrate the structure of Sphenophyllum:—

S. plurifoliatum.874, 882, 884, 893, 894, 897, 899, 901, 903, 908, 1893.
S. insigne.910, 914, 919, 921, 922, 924, 926, 1420, 1898.
Sphenophyllostachys.1049A–1049C, 1898.]

B. Types of vegetative branches of Sphenophyllum.

1822.Sphenophyllites emarginatus, Brongniart[895].
1828.Sphenophyllum emarginatum, Brongniart[896].
1828.Sphenophyllum truncatum, Brongniart[896].
1828.Rotularia marsileaefolia, Bischoff[897].
1862.Sphenophyllum osnabrugense, Römer[898].