Lady Isabel Browne. 
*3 
THE PHYLOGENY AND INTER-RELATIONSHIPS OF 
THE PTERIDOPHYTA. 
By Lady Isabel Browne. 
VI.—FILICALES— Continued. 
Loxsomace^e. 
As. the order of the Loxsomaceae contains only one species we 
may at once consider its affinity to the preceding orders of the 
phylum. The exarch solenostele of Loxsoma might well be derived 
from the simpler Botryopterideae, especially if the latter were, as 
the writer believes, primitively exarch. The fronds of many 
members of the fossil order were, however, more complex, in that 
they branched in more than one plane. The sporangia of both 
orders differed strikingly in their disposition on the frond, and in 
the structure of the sporangial wall and annulus. Therefore, 
though Loxsoma may well be descended from allies of the Botryo¬ 
pterideae it would be unwise to assert a direct affinity between it 
and the latter order. 
Both Mr. Gwynne-Vaughan and Professor Bower admit that 
Loxsoma shows a certain relationship to the Hymenophyllaceae, in 
which order it was formerly included; but they consider that it 
approaches closer to certain Cyatheaceae (19). Professor Bower 
points out that the texture of its leaf, the dehiscence of its sporangia, 
their structure and low output of large spores, are against such an 
affinity ; but he states that, putting aside the low output of spores, 
the Hymenophyllaceae might have arisen from such a type as 
Loxsoma , and that in this connection the anatomy of its rhizome 
should be interesting (6). Since its rhizome is now known to be 
solenostelic the protostelic Hymenophyllaceae cannot have been 
derived from Loxsoma. Further Loxsoma cannot be directly 
derived from filmy ferns, for its leaves are well developed. Both 
orders are clearly to be derived from protostelic forms, and these 
may have been in both cases exarch ; but if, as has been asserted, 
the Hymenophyllaceae are primitively endarch (2), (41), the exarchy 
of certain species of Trichomanes and Loxsoma is homoplastic and 
does not indicate close affinity. Since Professor Bower has shown 
that a basipetal succession of sporangia has arisen independently in 
several series of forms, this similarity may also be due to parallel 
development. 
The most striking similarities between the Schizaeaceae and 
