ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1918.tb00620.x

出版商:Blackwell Publishing Ltd    

年代:1918

数据来源: WILEY

摘要:

SUMMARYIn the first part of the paper additional evidence is brought forward as to the course of the leaf‐trace inCalamopitys americana.The trace, after separating from the reparutory strand, divides into two in traversing the zone of secondary wood. It thus differs from the trace ofC. 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.InC. annularisthe zone of primary xylem is almost if not quite continuous. The primary xylein‐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 pointsC. annularisagrees withC. americana.In the Halle specimen, a small branch referred by Solms‐Laubach toC. annularis, the medullary rays are narrow, resembling those ofC. fascicularisandC. Beinertiana.InC. Saturnithe 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, andC. Saturni, all hadKalymmxapetioles of very similar structure.InC. fascicularisthe leaf‐trace strands at their exit from the small pith are of large size, centrally mesarch and perfectly similar to those ofC. 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.InC. Beinertianathe 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 end arch. 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 ofC. fascicularisandC. Beinertianaunder the generic nameEristophyton; the conclusion is reached that, while generic separation may ultimately be justified, all the five species form a natural series, in whichC. Saturnioccupies, in certain respects, an intermediate position, betweenC. annularisandC. americanaon the one hand, andCfascicularisandC. Beinertianaon the other.Lastly, the affinities of the genus are discussed. While the wholeCalamopitysseries should remain in Oycadofilices, the nearest affinity being with the Lyginopteridese, throughHeterangium, the speciesC. fascicularisandC. Beinertianashow some advance towards the structure of Cordaitales and especially o

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1918.tb00621.x

出版商:Blackwell Publishing Ltd    

年代:1918

数据来源: WILEY