In a section of this species in the Williamson Collection[1161] the long axis of the stele has a length of 5 mm. and the diameter of the stem as a whole is 2·5 cm. The greater part of the extra-stelar tissue consists of large parenchymatous cells passing near the periphery into a band of darker and thicker-walled tissue.
Reniform vascular strands traverse the cortex in an obliquely ascending course on their way to the leaves, also smaller bundles, some of which are given off directly from the stele, while others are branches of the petiole vascular strands. The petioles described by Williamson as Rachiopteris insignis[1162] were afterwards recognised by him as those of Ankyropteris corrugata, though this conclusion was not published[1163]. Williamson’s species R. insignis must not be confused with Unger’s Culm species Arctopodium insigne, which Solms-Laubach[1164] refers to as Rachiopteris insignis. The leaf-bundle of Ankyropteris corrugata is at first reniform in contour ([fig. 314], C, P), but as it becomes free from the stem it gradually assumes the H-shaped form ([figs. 315–317]). This petiolar strand differs from that of Ankyropteris bibractensis ([fig. 313]) in the shorter and less strongly curved antennae; and, as Williamson first noticed, the tracheae are frequently filled with thin-walled parenchyma ([fig. 312], B). The existence of scale-leaves or aphlebiae like those of Ankyropteris scandens and A. Grayi has been recorded by Scott in A. corrugata[1165].
The section represented in [fig. 314], C, shows the relatively small size of the stele S in the stem of Ankyropteris corrugata. The main mass of the cortex consists of uniform parenchyma passing near the surface into darker and stronger tissue: two vascular bundles are shown in the cortex, one of which forms the conducting strand of a petiole, P, which has nearly freed itself from the stem: the other bundle, as shown by the examination of a series of sections, eventually passes into another leaf-stalk. A root of another plant has invaded the cortex at R, [fig. 314], C.
Fig. 314. Ankyropteris corrugata. R, intruded root; P, petiole; S, stele, Sv sieve-tubes.
- A, B. From a section in the University College Collection.
- C. After Williamson.
- D. From a section in the Williamson Collection (British Museum).
The form and structure of the stele is diagrammatically represented in [fig. 314], B. The outer portion (black) consists of a cylinder of scalariform tracheae in which the position of groups of smaller elements (protoxylem) is shown by the white patches. The xylem is thus seen to be mesarch. The prominent group of xylem on the lower right-hand side of the section consists of tracheae, cut across in an oblique direction, which are about to pass out as a separate strand. The centre of the stele is occupied by parenchymatous tissue in which are included scattered tracheae, either singly or in small groups. These medullary tracheae are rather narrower than those of the main xylem cylinder. A characteristic feature is the radial outward extension into the xylem of the medullary parenchyma, which tends partially to divide the tracheal cylinder into broad groups.
Fig. 315. Ankyropteris corrugata (Will.). Petiolar vascular strand. [From a section in the University College (London) Collection; after Tansley × 35.]
Fig. 314, A, enlarged from fig. B, a, shows the mesarch position of a protoxylem group, and a few of the parenchymatous cells of one of the narrow arms of the axial tissue. At Sv in fig. D a group of large sieve-tubes is seen separated from the xylem by a few parenchymatous cells, and beyond the sieve-tubes are some tangentially elongated cells. Both the sieve-tubes, Sv, and the flattened cells resemble tissues in a corresponding position in the steles of modern Osmundaceae.