xxv] 



ANKYROPTERIS 



459 



sieve-tubes, Sv, and the flattened cells resemble tissues in a 

 corresponding position in the steles of modern Osmundaceae. 



In a section of Ankyropteris corrugata in the Williamson 

 Collection the radial arrangement of the more external meta- 

 xylem elements suggests the addition of secondary tracheae'. 

 This suggestion of secondary thickening, a point which requires 

 much more thorough investigation, is interesting in relation to 

 a new type of stem named by Scott Botrychioxylon^, but not 

 yet fully described. This generic name has been given to 



a,' 



Fig. 316. 



Ankyropteris corrugata. Petiole, a, narrow xylem loop ; 6, spaces 

 in cortex. From a section in the Cambridge Botany School Collec- 

 tion. ( X 10.) 



a stem stele which closely resembles that of Ankyropteris cor- 

 rugata except in the regular radial arrangement of the peripheral 

 xylem elements. The name Botrychioxylon was chosen by Scott 

 because of the secondary xylem characteristic of the recent 

 genus Botrychuom (fig. 247, p. 322). 



In the petiolar vascular strand represented in fig. 315 the 

 narrow band of tracheae which forms a loop external to the 

 antennae is clearly seen, also the small-celled parenchyma 

 between the loops and the larger mebaxylem elements of the 



1 British Museum, section No. 245. Cf. figures by Williamson and Bertrand : 

 Williamson (77) PI. v. fig. 19; Bertrand, P. (09) PI. xii. fig. 87. 



2 Boott (07) p. 182; (08) p. 318. 



