316 FILICALES [CH. 



demand and supply as shown in the varying amount of con- 

 ducting tissue in the steles of different species. 



The leaf-trace in a great number of ferns is characterised by 

 its C -shaped form^ as seen in transverse section: this in some 

 genera, e.g. Matonia (fig. 237, A), is complicated by the spiral 

 infolding of the free edges of the C ; in other ferns (e.g. 

 some Cyatheaceae) (fig. 278, C) the sides of the C are incurved, 

 while in some species the xylem is broken up into a large 

 number of separate strands. 



An elaborate treatment of the leaf-traces of ferns was 

 published a few years ago by MM. Bertrand and Cornaille^ 

 in which the authors show how the various systems of vascular 

 tissue in the fronds of ferns may be derived from a common type. 

 As Prof Chodat^ justly remarks this important work has not 

 received the attention it deserves, the neglect being attributed 

 to the strange notation which is adopted^. 



The roots of ferns are characterised by a uniformity of plan 

 in marked contrast to the wide range of structure met with in 

 the stem and to a less extent in the leaves. The xylem may 

 consist of a plate of scalariform tracheae with a protoxylem 

 group at each end, or the stele may include six or more alter- 

 nating strands of xylem and phloem. 



II. Marattiales (Eusporangiate isosporous Filicales). 



The Marattiaceae, the single family of ferns included in the 

 Marattiales, comprise the genera Angiopteris, Archangiopteris, 

 Marattia, Danaea, and Kaulfussia, which are for the most part 

 tropical in distribution. These genera are characterised by 

 eusporangiate sori or synangia, the presence of stipules at the 

 base of the petioles, and by the complex arrangement of the 

 vascular tissue. In view of the fact that many fossil ferns 

 show a close resemblance to the recent Marattiaceae, the sur- 

 viving genera are briefiy described. The prothallus is green 

 and relatively large. 



' Gwynne-Vaughan (08). 



2 Bertrand and Cornaille (02). » Chodat (08) p. 15. 



* See also Pelourde (09) for an account of the anatomy of fern petioles. 



