452 COENOPTEEIDEAE [CH. 



A. scandens was found in association with the roots of a 

 Psaronius stem evidently petrified in situ as it burrowed, 

 like Tmesipteris, tropical aroids, and other recent plants, among 

 the living roots of the tree-fern. The stem, 10 — 11 mm. 

 in diameter, bore fronds with an H -shaped vascular strand, 

 small scale-leaves, and adventitious roots. The stele consists 

 of a five-angled cylinder of scalariform tracheae surrounding an 

 axial strand of parenchyma containing scattered tracheae of 

 smaller diameter. This axial tissue extends as a narrow strip 

 into each of the short and obtusely truncated arms (cf fig. 311). 

 A striking feature is the production of a shoot in the axil of the 

 foliage-leaves (fig. 310, D), a manner of branching characteristic 

 of Trichomanes (see page 365). 



Ankyropteris Orayi (Will.). Fig. 311. 



In describing this species, Williamson wrote — "That no 

 classification of these fossil ferns based solely upon transverse 

 sections of the petiolar bundles is or can be of much value, is 

 clearly shown when tested amongst those living ferns the 

 classification of which is chiefly based upon the sporangial 

 reproductive organs ^" This is a view entirely opposed to that 

 which inspires P. Bertrand's recent monograph. Whether the 

 value attached to the vascular structure of petioles as a basis 

 of classification is upheld or not, it is noteworthy that since 

 Williamson expressed his opinion, our knowledge of the anatomy 

 of ferns and of the value of anatomical evidence has enormously 

 increased. The slender stem^ of this Lower Coal-Measures 

 species agrees closely with that of A. scandens; it bore spirally 

 disposed fronds, scale-leaves, and roots. The stele has the form 

 of an irregular five-rayed star (fig. 311) in which the relative 

 length of the arms varies in different sections owing to the 

 separation of the distal ends to form leaf-traces. The axial 

 region is composed of parenchyma and associated narrow 

 tracheae, as in A. scandens. The xylem, with protoxylem 

 elements at the ends and especially at the angles of the arms 

 is completely surrounded by phloem. The cortex consists 

 1 Williamson (89) A. p.- 158. ^ jffin . gee also Soott (08). 



