Lady Isabel Browne. 
230 
THE PHYLOGENY AND INTER-RELATIONSHIPS OF 
THE PTERIDOPHYTA. 
By Lady Isabel Browne. 
V.—FILICALES. 
Botryopteridee:. 
In the first two orders of Ferns to be considered here, the 
fossil Botryopterideae and the Hymenophyllaceae, we find exarch and 
endarch protostely. This makes it convenient to discuss the anatomy 
of the stem in both orders at the same time; but in so doing it is 
necessary to guard against prejudging the question of the degree of 
affinity between them. Dr. Scott divides the fossil order into the 
Botryoptereae, in which the stele is more or less circular, and the 
Zygoptereae, in which it is more or less deeply lobed. In the latter 
group, including the genera Zygopteris, Asterochlaena, and Anachoro- 
pteris, the stele consists of two kinds of wood, the so-called 
external and internal xylem. The former is larger-celled, except at 
the ends of the projecting arms or rays ; but the inner part of the 
stele consists of parenchyma, embedded in which are groups of 
small tracheides (24). It is interesting to compare these more 
complex steles with those of Botryopteris, Tubicaulis and Grammato- 
pteris, members of the Botryoptereae. In Zygopteris corrugate we 
have a form possibly intermediate between the two types, for here 
we have the same groups of internal tracheides embedded in 
the parenchyma and surrounded by external xylem. But while the 
internal tissue forms angles projecting slightly into the external 
wood, the outline of the latter and of the stele remains circular, 
except just previous to the departure of the leaf-trace. As regards 
the position of the protoxylem, Miss Stopes, who investigated 
Tubicaulis, states that though the protoxylem is not particularly 
well differentiated, we may safely say that in that genus the whole, 
or nearly the whole, of the wood was centripetal (29). The 
Permian Grammatopteris was reported by Renault to have an exarch 
protostele, while Botryopteris is said to be endarch (24). Among 
the HymenophyllaceEe, some species, e.g., Trichomanes scandeus, 
possess an exarch protostele containing a few parenchymatous 
cells. Others, including T. reniforme, have a central protoxylem 
embedded in parenchyma and surrounded by two bands of tracheides. 
