438 COENOPTERIDEAE [CH. 



In the recent ferns Helminthostachys and Botrychium, and, as 

 Oliver notices, in the microsporangia of the Australian Cycad 

 Bowenia spectabilis, vascular strands extend aJmost to the 

 sporogenous tissue, but the fossil sporangium is unique in 

 having a tracheal layer in immediate contact with the spores. 

 These xylem elements may, as Oliver suggests, have served the 

 purpose of conveying water to the ripening spores. 



Botryopteris hirsuta (Will.)'. 



This English species has a slender axis bearing numerous 

 leaves with petioles equal in diameter to the stem. The surface 

 of the vegetative organs bears large multicellular hairs. The 

 leaf-traces resemble those of B. forensis, but the projecting teeth 

 which terminate in protoxylem elements are less prominent 

 than in the French species ; the petioles were named by Felix 

 Rachiopteris tridentata^. As a leaf- trace passes into the stele 

 of the stem the three protoxylem strands unite and take up an 

 internal position in the solid stele. The stele may, therefore, 

 be described as endarch. The small tracheae at the edge of 

 the stele supply the xylem strands of adventitious roots. 



Sporangia similar to those of B. forensis have been found in 

 association with the English species. 



Botryopteris cylindrica (Will.). Fig. 305. 



A plant originally described by Williamson' from the Lower 

 Coal-Measures of England as Rachiopteris cylindrica (fig. 305) 

 and afterwards more fully dealt with by Hick*, has a slender 

 stem with a cylindrical stele characterised by well-defined 

 central protoxylem elements in one or two groups. The leaf- 

 traces are semi-lunar in section with the protoxylem on the 

 flatter side. The stele of Botryopteris cylindrica (fig. 305, A) 

 is more cylindrical in section than that of B. ramosa (fig. 306) 

 and shows more clearly the differentiation into smaller central 

 and larger peripheral tracheae. In the section reproduced in 

 fig. 305, B the stele is giving off a branch almost identical in 



1 Soott, D. H. (08). 2 Felix (86) A. 



a Williamson (78) A. p. 351. * Hick (96). 



