Fig. 109. Sphenophyllum emarginatum (Brongniart).
From a specimen in the Collection of Mr R. Kidston, Upper Coal-Measures, Radstock. ⅚ nat. size.
This species of Sphenophyllum bears verticils of six or eight wedge-shaped leaves varying in breadth and in the extent of dissection of the laminae; they are truncated distally, and terminate in a margin characterised by blunt or obtusely-rounded teeth, each of which receives a single vein. The larger leaves are usually more or less deeply divided by a median slit. The narrow base of each leaf receives a single vein which branches repeatedly in a dichotomous manner in the substance of the lamina. Several drawings have been given by Sterzel[899] in a memoir on Permian plants, showing the variation in leaf-form in Sphenophyllum emarginatum, but as Kidston[900] and Zeiller[901] have pointed out Sterzel’s specimens probably belong to S. cuneifolium (Sternb.).
Branches are given off singly from the nodes, and the cones are borne at the tips of branches or branchlets. The cone of S. emarginatum agrees very closely with that of S. cuneifolium, and is of the same type as that shown in fig. 108. The small branch of S. emarginatum represented in fig. 109 does not show clearly the detailed characters of the species, as the leaf-margins are not well preserved.
In one of the largest specimens of this species which I have seen, in the Leipzig Museum, the main stem has internodes of about 3·9 cm. in length, from which a lateral branch with much shorter internodes is given off from a node.
It is important to notice the close resemblance, as pointed out by Zeiller, between some of the narrower-leaved forms of S. emarginatum and S. cuneifolium (Sternb.)[902]; but in the latter species the margins of the leaves have sharp, and not blunt teeth.
The cone described and figured by Weiss[903] as Bowmanites germanicus, since investigated by Solms-Laubach[904], must be referred to this species. Geinitz[905] figured a cone in 1855 as that of S. emarginatum, but his determination of the species is a little doubtful. Good figures of the true cone of S. emarginatum have been given by Zeiller[906] in his Flore de Valenciennes, as well as in his important memoir on the fructification of Sphenophyllum.
LEAVES.
2. Sphenophyllum trichomatosum Stur. Fig. 110, B.
The finely-divided leaves of the single whorl shown in fig. 110, B (from the Middle Coal-Measures of Barnsley, Yorkshire), afford an example of a form of Sphenophyllum which is represented by such species as S. tenerrimum Ett.[907], S. trichomatosum Stur[908], and S. myriophyllum[909] Crép. Probably the specimen should be referred to S. trichomatosum, but it is almost impossible to speak with certainty as to the specific value of an isolated leaf-whorl of this form. It has long been known that the leaves of Sphenophyllum may vary considerably, as regards the size of the segments, on the same plant; and the occurrence of such finely-divided leaves has lent support to an opinion which was formerly held by some writers, that Asterophyllites and Sphenophyllum could not be regarded as well-defined separate genera. This heterophylly of Sphenophyllum has thus been responsible for certain mistaken opinions both as to the relation of the genus to Calamocladus[910] (Asterophyllites), and as regards the view that the finely-divided laminae belonged to submerged leaf-whorls, while the broader segments were those of floating or subaerial whorls.
There is a very close resemblance between some of the deeply-cut and linear segments of a Sphenophyllum and the leaves of Calamocladus, but in the former genus the linear segments are found to be connected basally into a narrow common sheath. The assertion[911] that the deeply-cut leaves occur on the lower portions of stems is not supported by the facts. Kidston[912] has pointed out that the cones are often borne on branches with such leaves, and the same author refers to a figure by Germar, in which entire and much-divided leaves occur mixed together in the same individual specimen. M. Zeiller recently pointed out to me a similar irregular association of broader and narrower leaf-segments on the same shoots in some large specimens in the École des Mines, Paris. Cones of Sphenophyllum tenerrimum have been figured by Stur[913] and others; they are characterised by their small size and by the dissection of the slender free portions of the narrow bracts[914].