62 
Scott. — On a Palaeozoic Fern , the 
exhaustive and admirable account (Gordon, ’ll), has a solid xylem without 
any parenchyma, but there is a marked differentiation between the inner 
and the outer xylem ; the former consists of smaller elements, which are 
quite short, and presumably served for the storage rather than the conduc- 
tion of water. The complex structure of the petiole shows beyond doubt 
that the plant is a Zygopterid ; Dr. Gordon regards the stem-structure as 
the most primitive yet known in the family. So far as the solid xylem is 
concerned this may well be true ; in the shortening of the internal tracheides, 
however, Diplolabis shows a differentiation not yet observed in Ankyropteris , 
where these elements are, usually at least, of the ordinary elongated form. 
Also, as Dr. Gordon has pointed out, Diplolabis and Metaclepsydropsis have 
quadriseriate pinnae, while in Ankyropteris they are biseriate. It therefore 
appears that these three genera cannot belong to the same direct line of 
descent. Dr. Gordon’s suggestion (Gordon, ’ll 2 ) that Diplolabis and Meta - 
clepsydropsis led on to Zygopteris Grayi involved the assumption that the 
latter species is an Etapteris , whereas, as we have seen, it belongs to 
Ankyropteris. Of the stem of Etapteris we know nothing as yet. 
I am inclined to agree with Dr. Gordon’s general line of argument in 
deriving the stem-structure of Zygopterideae from a simple protostele like 
that of Botryopteris , though, as we shall see presently, Dr. P. Bertrand takes 
a totally different view of the relationships. 1 
The most interesting comparison, perhaps, is that between Ankyropteris 
Grayi and Aster ochlaena, a genus very imperfectly known until 1911, when 
Dr. P. Bertrand published a magnificent monograph on the Permian species 
Asterochlaena laxa , Stenzel. This fine fossil is on a much larger scale than 
our Ankyropteris , the stem (apart from the leaf-bases) reaching 50 mm. in 
diameter. The xylem, as is well known, is of the most extreme stellate 
form, with long spidery arms. The number of xylem-arms at the periphery 
of the star ranges from eight to thirteen ; they anastomose towards the 
centre. There is, however, no relation between the form of the star and 
the phyllotaxis, for each xylem-arm gives off two or three series of leaf- 
traces ; the arrangement of the bi- and tri-lobed arms is irregular ; 
a unilobed arm has only once been observed with certainty. The number 
of orthostichies ranges from twenty to twenty-seven ; in some specimens 
the phyllotaxis is whorled, in alternating verticils of ten or eleven members ; 
in the others it is described as ‘ subverticillate ’, the number of orthostichies 
being uneven. 
In spite of these striking differences from Ankyropteris , many equally 
remarkable points of agreement exist. There is a ‘ mixed pith ’ at the 
centre of the star, and from this, median protoxylem-bands radiate, passing 
up the middle of each arm; where the arm forks the protoxylem-bands 
1 The discussion of the curious stem of Zygopteris Kidstoni (P. Bertrand, ’ll, p. 55), which 
is described as having a stellate solid xylem, will be best postponed till fuller information is available. 
