314 STUDIES IN FOSSIL BOTANY 



well as on the stem. A single bundle enters each 

 appendage, and then divides into two, three, or four 

 strands. An example from Z. corrugata is shown, in 

 transverse section, in Fig. 117; it has just detached 

 itself from the base of a petiole, and contains two 

 bundles. The morphology of these curious organs, 

 which in some respects recall the Aphlebiae of other 

 Palaeozoic Ferns and Pteridosperms, requires further 

 elucidation. 



The stem also bore adventitious roots ; the vascular 

 strands supplying them can be distinguished from those 

 of the scales by their more horizontal course. 



Such evidence as we possess from other species as 

 to the form of the foliage-leaf will best be considered 

 at a later stage, after the fructifications have been dealt 

 with. The petiolar structure is better shown in some 

 other forms of Zygopteris, the stems of which are not 

 in all cases known. Thus in a petiole named Z. 

 Lacattii by M. Renault, which is frequent in the English 

 Coal-measures, as well as in those of France, all the 

 tissues are sometimes well preserved. In this case the 

 tracheides are generally pitted rather than scalariform, 

 a character which was clearly very variable in this 

 group, though of considerable constancy in other 

 families. The subject of the so-called tracheides of 

 Palaeozoic Ferns and allied groups requires further 

 investigation in the light of Mr. Gwynne-Vaughan's 

 remarkable discovery that the scalariform elements of 

 Ferns are not tracheides, but a peculiar form of vessel, 

 in which not only the closing membranes of the pits, 

 but the middle lamellae of the cell-walls are absorbed, 

 leaving only the bars of thickening, connected by the 



