236 Lady Isabel Browne. 
as a closed ring, is in both varieties comparable to Botryopteridean 
traces (32). The dimorphism of the fronds of most Botryopteridese, 
and the fact that these fronds show no indications of dichotomy are 
points in which the fossil order seems to be less primitive than the 
recent. These differences, coupled with the much slighter structure 
of the sporangia, and the position of the annulus, would seem to 
the writer to forbid the derivation of the Hymenophyllaceae from 
the Botryopterideae, but the similarities between the two orders 
warrant the supposition that both were derived from the group of 
simple monostelic Palaeozoic Ferns, at present ill-defined, to which 
Mr. Arber has given the name of Primofilices (1); the Botryo¬ 
pteridese would be an important but specialized order of the group, 
while the Hymenophyllacese are probably descended from less 
specialized forms (24). 
SCHIZAJACE/E. 
. Though the course of evolution of the stele in the Schizaeacete 
is still very variously interpreted, it seems to be generally 
agreed that the stele of Lygodium is the most primitive in 
the order. It is a protostele, and the first-formed elements are 
indeterminate, but show a tendency to assume a peripheral position* 
In Schizcea digitata the rhizome contains a woody ring enclosing a 
pith ; in S. dichotoma and 5. malaccana endodermal pockets are 
developed in connection with some of the leaf-gaps ; as in Lygodium 
the protoxylem is scattered (4). Besides the endodermal pockets, 
Mr. Boodle records the occasional occurrence, in Schizcca digitata, 
of an isolated inner endodermis and local patches of internal 
tracheides, connected with or free from those of the woody ring (6). 
5. malaccana sometimes, though rarely, also possesses an internal 
strand, or still more rarely two such strands in its pith. But far 
more often the central parenchyma also contains an internal endo¬ 
dermis ; this endodermis may be a mere rod of cells or it may 
enclose one or more cells (35). Aneimia mexicana and a few other 
species are truly solenostelic, while A. Phyllitidis and Mohria are 
dictyostelic, the meristeles being concentric and containing internal 
and external phloem (3). 
It seems clear from Dr. Jeffrey’s and Mr. Gwynne-Vaughan’s 
researches on the ontogeny of the Ferns that the solenostele was 
derived from the protostele (20), (16). This conclusion is now widely 
accepted for the majority of ferns (33), (13). The same writers 
have shown that the dictyostelic type of stem usually arises from a 
