XXXIIl] CORDAITES 229 



interprets the narrower tracheids (occupying a position similar 

 to those in fig. 465) in some sections of a leaf identified with C. 

 principals from Grand' Croix, as an inner sheath of transfusion 

 elements ('primitive transfusion tissue') possibly derived from 

 the centripetal xylem with which it is clearly connected at the 

 sides precisely as in fig. 465; but in the Grand' Croix leaf the 

 phloem is enclosed within the sheath of narrower tracheids and 

 not external to it as it is in the section shown in fig. 465 and in 

 a section of C. lingulatus figured by Dr Stopes. It is, however, 

 difficult to recognise any fundamental difference between the 

 'inner transfusion tissue' and centripetal xylem. The cells of 

 the outer sheath in Dr Stopes's specimens of C. principalis have 

 bordered pits on their walls and this character is mentioned also 

 by Renault in other specimens. 



Prof. Lignier 1 has described the structure of fragments of 

 adult leaves from the Stephanian of Grand' Croix (Loire) which 

 he refers to Cordaites lingulatus, and the same author gives an 

 interesting account of the anatomical features of a bud of the 

 same species. The bud, which resembles in general appearance 

 that of Dolerophyllum (fig. 430, p. 133) is 3 cm. long, oval in 

 transverse section as the result of compression and consists 

 of four convolute leaves and a piece of a fifth. The outer leaves 

 have 75 to 80 veins : the inner laminae are sinistral in their 

 curvature while the three outer leaves are dextral. In the second, 

 the first in which the tissues are recognisable, the small desmogen- 

 strands afford some evidence that the phloem preceded the 

 xylem in the order of differentiation as is often the case in recent 

 plants. The first tracheids occur almost in the centre of the 

 desmogen-strand and to these are added the other tracheids of 

 the centripetal xylem, the oldest elements being spiral, the next 

 scalariform and the later tracheids reticulate. The centrifugal 

 xylem is formed at a later stage, and at about the same time are 

 differentiated the elements called by Dr Stopes the inner sheath 

 and by Lignier the 'bois diaphragmatique.' Lignier also describes 

 the development and structural features of the other tissues of 

 the young leaves and compares the anatomical features of the 



1 Lignier (13 2 ). 



