246 Lady Isabel Browne. 
by Mr. Tansley and Miss Lulham (37). They point out that the 
primary division of the frond is a dichotomy in the angle of which 
a middle pinna is developed ; and that the young plant shows a 
tendency to produce fronds that branch dichotomously. They 
suggest that the peculiar fan-like adult frond of Matonia arises “ by 
dichotomy of the primary forks and the repeated dichotomy of the 
lower member only of each successive fork, the upper member in 
each case and the lower also of the last fork, becoming a pinna ” 
(37). They point out that on this view the two main recurved 
branches of the frond are sympodial structures composed of the 
bases of lower members of successive dichotomies, and that this is 
suggested by their scorpioid form. Further, the hypothesis that 
this type of frond is a modification of a dichotomous one enables 
us, as the same writers remark, to bring Matonia into relation with 
Gleickenia, several species of which show a tendency for the lower 
members of the dichotomy to divide again, while the upper ones 
form pinnae. The middle pinna of Matonia, whatever its origin, 
may be compared with the bud occupying the axil of the dichotomy 
of the fronds of Gleichmia. Thus there seems good reason for 
supposing that Matonia may have originated from the simplest 
Gleicheniaceae, or from forms very close to them. Anatomically 
Matonia is much more complex, but if the anatomy of the Mesozoic 
Matonineae were known they might serve to bridge this gap. 
Cyatheacb/e and Polypodiace.®. 
The Cyatheaceae and Polypodiaceae are clearly closely related 
and it is convenient to discuss their anatomy at the same time. 
Probably the most primitive type of stele found in either order is 
that known as the Lindsaya- type. Its structure is practically that 
of a protostele, but embedded in the dorsal part of the xylem is a 
strand of phloem. Mr. Tansley and Miss Lulham point out that 
the “ nodal islands ” of Gleickenia indicate the manner in which the 
more bulky phloem strand of Lindsaya may have arisen (36). 
Indeed we can see that if a nodal island were to become somewhat 
larger, to consist only of phloem and to be continued through the 
internode until it met another nodal island we should have a 
structure closely similar to the Lindsaya- stele. It has been shown 
that nodal islands are formed in connection with leaf-gaps; this is 
presumably phylogenetically true of the Lindsaya phloem-strand, 
and explains the position of the latter near the dorsal surface of the 
rhizome. This Lindsaya- type occurs in several Polypodiaceous 
