97 
The Leaf-structure of Cordaites. 
bases his species. The exact size of the leaf is not mentioned by 
him, hut working from his figures we find it corresponds to ours, 
i.e., *4 mm. in thickness; as also does the distance between the 
bundles, both Renault’s and ours averaging ’45 mm. The only 
essential difference is in the presence of centrifugal xylem in 
Renault’s figures, a point which we have already endeavoured to 
explain. The two leaves in this case coinciding so exactly in all- 
respects, it seems needless to found a new species to receive the 
one under consideration. 
We shew for comparison a cross section of a bundle and 
adjacent parts of the leaf of C. lingulatus (phot 1.) which has 
undoubted centrifugal xylem ; with the phloem, which unfortunately 
does not show up well, in its proper position outside it. 
As a Cordaitean character possibly too much weight may have 
been attached to the presence of centrifugal xylem in the foliar 
strand. There are three sets of original figures of structure 
specimens of Cordaites; the well-known ones of Renault 1 , those 
of Grand’ Eury 3 , and those of Felix 3 . Of the six species figured by 
Renault, three only (C. angulostriatus, C. lingulatus, and C. princi¬ 
palis), are described as possessing centrifugal xylem, and if, as we 
are inclined to suppose, the last is without it, there remain but 
two. Of Grand’ Eury’s three examples none shew it, and of 
Felix’s three figures one only shews it clearly, one has cells which 
might be interpreted in this sense, and one has none. So that on 
the whole, the majority of known Cordaitean leaves appear to be 
without centrifugal xylem. 
Hence there seems to be some resemblance between the 
leaf bundles of most species of Cordaites and the petiolar bundles of 
Medullosa which, as is well-known, are exarch. They are of some¬ 
what simpler type in Myeloxylon radiation (the petiole of a Medullosa), 
the xylem consisting only of spiral and finely reticulate tracheides, 
the large pitted elements found in Cordaites and Cycas not being 
represented; the sheath also is simpler and is composed of fibres 
differing in no important respect from those surrounding the 
mucilage ducts, and hence having no affinity with transfusion-tissue. 
1 Renault, Structure compare de quelques tiges de la Flore 
Carbonifere, pi 16. Cours de Bot. fossile I., plate 12. These are 
the same figures. 
* Grand’ Eury, Flore carbonifere de Dept, de la Loire et du 
Centre de la France, pi. xviii., and Geol. du Card. 
3 Felix, Uutersucli. fiber den iimern Bau Westfalisches Carbon 
planzen, plate iii. 
