14 Lady Isabel Browne. 
Loxsoma, viz., the solenostele and C-shaped trace are very common 
in the Ferns. The former certainly and the latter possibly origi¬ 
nated independently in the two orders ; but the exarchy of both 
may well have been inherited from an exarch protostelic ancestor. 
Loxsoma Cunninghami, the only species of the Loxsomacese, 
has an exarch solenostele and a C-shaped leaf-trace. According to 
the views expressed by the writer the exarchy of its stele is the 
principal character in which Loxsoma is more primitive than the 
Gleicheniaceae. Since the solenostele of Gleichenia pectinata was 
clearly evolved within the order it seems probable that both 
orders have been derived from protostelic forms of mainly 
Gleicheniaceous type, but with entirely centripetal wood. The 
principal changes which, on this hypothesis, have occurred in the 
evolution of a form like Loxsoma, viz., the evolution of solenostely 
from protostely, of pinnate from dichotomous fronds, of the 
“ gradate ” from the “ simultaneous ” sorus, have been traced in 
several evolutionary series of forms and may be regarded as well 
established evolutionary processes (16), (24), (20), (36), (31), (6). 
Solenosteles have been shown to have arisen very frequently 
in the Ferns; those of Loxsoma and of Matonia almost certainly 
originated independently, for it is clear that the ancestors of 
Loxsoma began to diverge from the Gleicheniaceous type before 
those of Matonia had acquired any centrifugal xylern. This is 
borne out by the considerable differences in the fronds and sori of 
Matonia and Loxsoma. 
Loxsoma is perhaps most closely allied to the Cyatheaceas and 
Polypodiaceas. Mr. Gwynne-Vaughan has pointed out that anato¬ 
mically the genus comes nearest to the more primitive members of 
these orders, to the simpler Dicksonias and Davallias (19). The 
similarity extends to the solenostely, to the structure of the leaf- 
trace, to the pinnate division of the fronds and to other less 
important points. Professor Bower recognizes this affinity not only 
in the anatomy, but also in the habit, the form of the indusium and 
the “gradate” sorus (6). But since Loxsoma is exarch the centri¬ 
fugal wood of the Polypodiaceae and Cyatheaceae must (though 
these orders are in other respects very close to Loxsoma ) have been 
developed since the two stocks began to diverge from one another. 
OSMUNDACE.E. 
In the recent Osmundaceae the centre of the stem is occupied 
by a pith, embedded in the periphery of which is a circle of woody 
strands, separated by medullary rays, through which the continuous 
ring of phloem may project slightly inwards. In a few species the 
