Notes on Calamopitys, Unger.

Abstract

In the first part of the paper additional evidence is brought forward as to the course of the leaf-trace in Calamopitys americana. The trace, after separating from the reparatory strand, divides into two in traversing the zone of secondary wood. It thus differs from the trace of C. Saturni, in which division is only completed beyond the zone of thickening. The second part of the paper is devoted to a re-examination of the five species. In C. annularis the zone of primary xylem is almost if not quite continuous. The primary xylem-strands are, as a rule, eccentrically mesarch, the protoxylem lying nearer the outer side of the strand. Tubular elements, which are probably medullary tracheides, are present in the pith, indicating a protostelic structure. Each leaf-trace strand, on its exit from the wood, is surrounded by its own zone of secondary xylem. In all these points C. annularis agrees with C. americana. In the Halle specimen, a small branch referred by Solms-Laubach to C. annularis, the medullary rays are narrow, resembling those of C. fascicularis and C. Beinertiana. In C. Saturni the primary xylem-strands are found to be completely isolated; there is no continuous xylem-ring. The xylem-strands are, as a rule, centrally mesarch, with the centrifugal and centripetal portions equally developed. There is little or no indication of medullary tracheides. The three species, C. americana, C. annularis, and C. Saturni, all had Kalymma petioles of very similar structure. In C. fascicularis the leaf-trace strands at their exit from the small pith are of large size, centrally mesarch and perfectly similar to those of C. Saturni. Lower down in their course they diminish in size and the centripetal portion of the xylem becomes much reduced. The protoxylem of the leaf-trace divides into two in passing through the zone of secondary wood. The wood has narrow medullary rays and is generally of a Cordaitean type. Its inner layers consist of short, wide tracheides, suggesting a water-storing function. In C. Beinertiana the pith is large and contains sclerotic nests. The xylem-strands are similar to those of the preceding species, except that in the lower part of their course they become actually endarch. Division of the protoxylem has not been observed. The wood has a Cordaitean character. A synopsis of the five species is given on p. 221. The affinities of the species are then considered, with reference to Dr. Zalessky's proposed separation of C. fascicularis and C. Beinertiana under the generic name Eristophyton; the conclusion is reached that, while generic separation may ultimately be justified, all the five species form a natural series, in which C. Saturni occupies, in certain respects, an intermediate position, between C. annularis and C. americana on the one hand, and C. fascicularis and C. Beinertiana on the other. Lastly, the affinities of the genus are discussed. While the whole Calamopitys series should remain in Cycadofilices, the nearest affinity being with the Lyginopterideæ, through Heterangium, the species C. fascicularis and C. Beinertiana show some advance towards the structure of Cordaitales and especially of the family Cordaiteæ.