380 Farmer and Hill . — Arrangement and Structure 
we look on the peripheral mesh work as the representative of 
the siphonostelic cylinder in them. 
The foliar gaps are large, and the leaf-trace strands plainly 
correspond exactly in their origin with those of the two genera 
already described. The two strong lateral steles, which in 
our specimens leave the outer edges of the lower margin of 
each gap* clearly represent the original forking trace which we 
may confidently expect the young sporophyte will be found 
to possess. Lying between these, and originating exactly 
as in Angiopteris , are a number of subsidiary strands, which 
anastomose both with each other and with the strong principal 
lateral forks of the original dichotomising petiolar steles. 
Turning to the lower surface of the stem, we find diamond- 
shaped gaps resembling foliar gaps, but in accordance with 
the dorsiventral habit, no leaf-traces take their origin from 
them. This occurrence of gaps on the lower surface is of 
interest as perhaps indicating that the marked dorsiventrality 
which Kaulfussia now exhibits, may have been acquired from 
a radially formed ancestor, the interior anatomical characters 
corresponding to such a disposition having been retained. 
Both Marattia and Angiopteris also exhibit a tendency to 
dorsiventrality, but it is not very marked in young plants. Thus 
in this group, we find the skeletal framework clearly showing 
the original type from which they have been derived, although 
in external conformation the departure from the radial character 
has in Kaulfussia become very complete. An interesting 
parallel may be drawn between the Marattiaceae and the 
Ophioglossaceae, in which much the same range of variety 
can be traced. In Helmin thostachys, however, the dorsiven- 
trality which is quite as pronounced as in Kaulfussia , has also 
affected its internal structure, and to a more profound extent. 
There are no gaps at all in the lower surface of its siphono- 
stele, and the roots are restricted to the sides and lower 
surface of the vascular cylinder. 
In Kaulfussia , however, the commissural strand, as in the 
other genera of Marattiaceae, also may give rise to roots, 
which burrow through the parenchyma of the stem and pass 
