ZYGOPTERIS 307 



the evidence as to external habit is comparatively 

 scanty. 



The stem of Zygopteris Grayi was from 10 to 

 1 5 mm. in diameter, and no doubt attained a 

 considerable length. In fact, Stenzel regarded his 

 closely similar form as a climbing plant, and hence 

 named it Z. scandens, for he always found the stems 

 and petioles of his specimens intermixed with the 

 crowded roots of a PsaroniuSj among which he. 

 believes it to have scrambled, much in the same 

 way as a Tmesipteris lives among the aerial roots of 

 the New Zealand Tree - ferns at the present day. 

 From the stem large petioles (little inferior to the 

 stem in diameter) were given off, at considerable 

 intervals ; the phyllotaxis was a spiral one, and in 

 certain cases, at any rate, the arrangement was clearly 

 on the ^ system (see Figs. 115 and 1 1 6). 



In all the known Botryopterideae the stem was 

 traversed by a single vascular cylinder ; this mono- 

 stelic structure, exceptional among recent Ferns, appears 

 to have been more widely prevalent among those of 

 Palaeozoic age. 



In our Zygopteris the stele has a very characteristic 

 structure ; its general form follows that of the wood, 

 which in section has the outline of an irregular five-rayed 

 star (see Figs. 1 1 5 and 1 1 6). These rays are of very 

 unequal length ; the comparison of successive transverse 

 sections shows that the shortest are those which have 

 just given off a leaf-trace (Fig. 116, 1), while the 

 longest are those which are just about to do so 

 (Fig. 116, 5). From the position of the leaf- traces 

 and their relation to the prominent corners of the 



