XXV] ZYGOPTEREAE 443 



of the stem and that of the petiole is probably another mark 

 of a more primitive type. 



In these three types, Grammatopteris, Tubicaulis, and Botryo- 

 pteris, we have monostelic plants, for the most part of very small 

 size, with leaf-traces varying in shape from the oblong band-form 

 in Grammatopteris, and the oval form of Botryopteris antiqua, to 

 the CO type represented in its most pronounced form by B.forensis. 

 In -several species the stem stele is endarch. Our knowledge 

 of the leaves is very meagre : in B. forensis they were repeatedly 

 branched and apparently bore small fleshy pinnules ; the spo- 

 rangia, though differing from those of recent ferns, may be 

 compared with the spore-capsules of Osmundaceae as regards 

 the structure of the annulus. The abundance of hairs on the 

 stems and leaves of some species, the tracheal sheath in the 

 sporangium described by Oliver' as Tracheotheca (=Botryopteris'?), 

 and the apparent absence of a large well-developed lamina, 

 may perhaps be regarded as evidence of xerophilous conditions. 



II. Zygoptereae. 



Corda^ proposed the generic name Zygopteris for petrified 

 petioles from the Permian of Saxony, included by Cotta in his 

 genus Tubicaulis, which he named T. prim,arius. Corda's genus 

 has been generally used for petioles of Palaeozoic ferns charac- 

 terised by a vascular strand having the form of an H in 

 transverse section (fig. 308, D). Since the generic name was 

 instituted, information has been obtained in regard to the 

 nature of the stems which bore some of the petioles of the 

 Zygopteris type ; and for other species of Zygopteris, the stems 

 of which are still unknown, new generic names have been 

 proposed. P. Bertrand^ retains Zygopteris for one species only, 

 Z. primaria. Fig. 308, D, shows the character of the petiolar 

 vascular strand ; the chief points are the comparatively long 

 cross-pieces (antennae of P. Bertrand) inclined at an angle of 

 45° to the plane of symmetry of the petiole axis, and the groups 



1 Oliver (02). ^ Corda (45) A. ; see also Stenzel (89) p. 26. 



3 P. Bertrand (09) pp. 136, 212. 



