28 COENOPTERIDACEAE [ch. 



Stauropteris 



It is otherwise with Stauropteris oldhainia Binney, a fossil of frequent 

 occurrence in nodules of the Coal Measures; another species (5. burntis- 

 landicd) has been described by P. Bertrand from the Lower Carboniferous 

 of Burntisland. Though the stem of Stauropteris is unknown, the structure 

 of the petiole and of the upward ramifications of the erect frond has been 

 followed out in detail, as well as the form and characters of the distal 

 sporangia. The frond had a more nearl)' radial structure than any of the 

 Zygopterideae, though it is constructed on a plan similar to that of the 

 four-rowed types. The genus is held to be somewhat apart from that 

 family, but the natural relationship to it can hardly be in doubt. The 

 frond was highly compound without any expanded lamina. Its general 

 habit was probably shrubby, with numerous upward-directed branchlets of 





Fig. 328. Clepsydropsis aiitiqiia Unger, var. c'x({'//a. The fuliar trace of a primary ])etiole, 

 with a ring of vascular tissue (S) separating off, destined to a secondary petiole. 

 l>p, peripheral loop, (x 70.) (After P. Bertrand.) 



almost cylindrical form supported by a central rachis. The structure of this 

 is shown in Fig. 329. Centrally the xylem is cruciform in section. It is 

 composed of four wedges often united at the centre, but they may be more 

 or less detached. A group of protoxylem lies peripherally near to the 

 outer margin of each, whence the supply for the successive pairs of pinnae 

 is derived alternately right and left. The xylem is surrounded by phloem 

 which intrudes between the wedges with groups of large sieve-tubes. The 

 whole vascular tract takes an almost quadrangular form in the upper regions 

 of the frond (Fig. 330). It is surrounded by a broad band of thick-walled 

 parenchyma limited by an epidermis with stomata; but the hypodermal 

 tract differs from the rest in being a lacunar tissue, probably photosynthetic. 

 It widens out in the upper regions, forming a considerable proportion of the 

 bulk of the branchlets. Comparison has been made with the similar photo- 

 synthetic tissue in Psiloturn. 



