Morphology of gymnosperms / by John M. Coulter and Charles J. Chamberlain.

  • Coulter, John Merle, 1851-1928.
Date:
[1910]
Catalogue details

Licence: In copyright

Credit: Morphology of gymnosperms / by John M. Coulter and Charles J. Chamberlain. Source: Wellcome Collection.

    35/494 (page 21)
    belong to Cycadofilicales, but they include forms known to be such (.Lyginodendron, Heterangium, Medullosa); others almost certainly such because of their evident relationships (Colpoxylon, Sutcliffia, Megaloxylon, Calamopitys, Cycadoxylon)-, and others possibly such because they are Cycadofilices. Each of the genera cited represents a stem family of the same name, except that Heterangium is included in the Lyginodendrineae (Lyginodendreae), and Colpoxylon and Sutcliffia in the Medullosineae (Medulloseae). Cycadofilicales are known to extend beyond the range of these stem genera, for seed- bearing fronds have been discovered the structure of whose stems is unknown. The stems already described, however, show a wide anatomical range for the group, being protostelic (Heterangium and Sutcliffia), siphonostelic (Lyginodendron, Megaloxylon, Cycadoxylon, etc.), and polystelic (Medullosa, Cladoxylon, Colpoxylon, etc.); while the xylem of the stem ranges from exarch (Sutcliffia), through mesarch (the general condition), to endarch {Cycadoxylon). The leaf traces also range from the usual simple forking to a profuse branching and anastomosing. So far as vascular anatomy is concerned, therefore, the Cycadofilicales exhibit as wide a variation and the same kind of variation as do the existing ferns, and they add to these characteristics those of existing gymnosperms. THE LEAF OF CYCADOFILICALES To distinguish the leaves of Cycadofilicales among the innumerable paleozoic “fronds” that have been preserved is at present impossible. It has been suggested (60) that the prevailing dichotomy of paleozoic fronds may be indicative of Cycadofilicales rather than of ferns, but such a character cannot be used with any definiteness. In fact, Scott has said recently (82) that from the frond alone it cannot be told whether a paleozoic plant is a fern or one of the Cycadofilicales. The best that can be done is to select those leaves whose connection with stems or with seeds testifies to their nature. In this way most of the large frond genera have contributed representatives to the Cycado- filicales, but it may be that some of their other members are ferns. At least, so artificial an assemblage as a large frond genus would suggest such a possibility. The certain or probable cases of leaves belonging to the Cycadofilicales are as follows: