Boodle.—Anatomy of the Hymenophyllaceae. 489 
view of the filmy habit being primitive. The solid stele of 
Botryopteris , as the wood consists of tracheides only, resembles 
the stele found in the lower part of the seedling-stem of 
Trichomanes rather than the solid stele of T. spicatum , &c. 
The transition from root to stem structure has been in¬ 
vestigated by Leclerc du Sablon 1 in a young plant of Tricho¬ 
manes alatum. Described shortly, these are his results :—The 
root is diarch with no pith ; at a distance from the prothallus 
a pith may appear in the primary root, 01 may not; in the 
passage from root to stem, the number of tracheides increases, 
and the wood then forms a rounded mass completely sur¬ 
rounded by phloem 2 ; in the larger parts the tracheides 
increase further in number, then separate a little from one 
another, so that the whole of the wood is formed of tracheides 
mixed with unlignified parenchymatous cells; apart from 
further changes in thickness, the stele has then attained its 
mature structure. The stem of the young plant thus has 
a solid xylem-mass similar to T. spicatum or T. scandens. 
These developmental facts may mean that the solid xylem- 
mass is primitive, but it does not prove that the species may 
not phylogenetically have passed through a stage in which the 
mature stem may have been similar to that of T. reniforme 
or H. scabrum. T. alatum and other species with a solid 
stele may be cases in which the youth-form of structure is 
retained in the mature plant. 
In view of the probability (owing to varying conditions) 
that reduction has taken place in different series, especially 
in the genus Trichomanes , and that in this genus the change 
from creeping to upright habit, and perhaps to coriaceous 
habit has occurred, nothing weighty can be put forward with 
regard to the classification of the species. But a few facts 
may be pointed out. 
The two-banded Hymenophyllums agree well with one 
1 Leclerc du Sablon, Recherches sur la formation de la tige des Fougeres, Ann. 
des Sci. Nat., 7 e ser., t. xi, p. 11 
2 1 . c., Fig. 21. There is here no pith, and no parenchyma among the 
tracheides. 
