Fig. 321. Stauropteris oldhamia: a, sections of pinnae. (× 10. From a section in the Cambridge Botany School Coll.)
The rachis reproduced in [fig. 321] is surrounded by an enormous number of sections, some transverse, others more or less vertical, of branchlets of various sizes. Fig. 310, B, shows the three-rayed vascular axis of a branch of a lower order than those seen in fig. C, and the single vascular strands of still finer ramifications of the leaf. The extraordinary abundance of axes of different sizes, many of which are cut in the plane of branching, in close association with the rachises of Stauropteris affords a striking demonstration of the extent to which the subdivision of the frond was carried in a small space. The leaves must have presented the appearance of a feathery plexus of delicate green branchlets devoid of a lamina, some of which bore terminal sporangia. It may be that the delicate fronds were borne on a slender rhizome which lived epiphytically in a moist atmosphere on the stouter stems of a supporting plant.
The sporangia[1190] of Stauropteris oldhamia are exannulate and nearly spherical, with a wall of more than a single row of cells; they occur at the tips of slender and doubtless pendulous branchlets. The discovery by Scott[1191] of germinating spores ([fig. 323]) in a sporangium of this type supplies an interesting piece of evidence in favour of the fern nature of these reproductive organs. Similar germinating spores have been described by Boodle[1192] in sporangia of Todea.
Fig. 322. Sporangia of Stauropteris oldhamia. St, stomium: p, palisade tissue. (From Tansley, after D. H. Scott, from a drawing by Mrs D. H. Scott.)
Stauropteris burntislandica.
This Lower Carboniferous plant identified by Williamson with the Oldham plant from the Lower Coal-Measures is referred by Bertrand to a distinct species. In the structure of the rachis stele it agrees closely with Stauropteris oldhamia; the main vascular strand gives off four rows of branches, two from each side, and aphlebiae were present at the common base of each pair of pinnae. Mrs Scott[1193], who has recently described the sporangia of this species, speaks of one specimen in which germinating spores were found. The same author gives an account of some curious spindle-shaped bodies which she found in association with S. burntislandica. The nature of these organs is uncertain; Mrs Scott inclines to regard them as glands borne in pairs on lateral pedicels of the frond: she adopts for these the name Bensonites fusiformis proposed by Dr Scott. If there is a reasonable probability, as there certainly seems to be, in favour of connecting these organs with Stauropteris, it is legitimate to question the desirability of adding to the long list of names included in the group Coenopterideae.
Fig. 323. Germinating spores from a sporangium of Stauropteris. (From Tansley, after D. H. Scott.)