456 COENOPTERIDEAE [CH. 



A cylinder of thin-walled tissue encloses the xylem and in this 

 occur groups of large sieve-tubes (fig. 314, D, Sv). 



In a section of this species in the Williamson Collection^ 

 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^ were after- 

 wards recognised by him as those of Ankyropteris corrugata, 

 though this conclusion was not published ^ Williamson's 

 species R. insignis must not be confused with lingers Culm 

 species Arctopodivmi insigne, which Solms-Laubach* refers to as 

 Rachiopteris insignis. The leaf-bundle of Ankyropteris corru- 

 gata 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'. 



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 



1 No. 245. 



" Williamson (80) A. p. 507. » Scott (06). 



* Solms-Laubach (96). » Scott, D. H. (06) p. 519. 



