20 
Lady Isabel Browne. 
There is little affinity between the Osmundaceae and the 
Marsileaceae, but the latter and the Salviniaceae are usually classed 
together as the Hydropterideae. Though both are aquatic and 
heterosporous ferns they differ considerably. The Salviniaceae are 
anatomically simpler; their sporocarps appear to be indusial 
structures, not homologous with those of the Marsileaceae, which 
consist of metamorphosed leaf-segments. In the latter order the 
sori are bi-sexual, in the former unisexual Mr. Arber has pointed 
out that the heterospory of the Hydropterideae originated indepen¬ 
dently of the heterospory that preceded the evolution of a seed (I). 
The differences between the Salviniaceae and Marsileaceae seem, 
however, not to exclude the possibility that heterospory originated 
independently in each order. Though Dr. Campbell does not 
expressly assert such an opinion, it should be noted that he derives 
the Salviniaceae and Marsileaceae from different homosporous 
orders (13). 
PSARONIE/E. 
The Psaronieae are fossil stems from the Upper Carboniferous 
and Permian rocks. In the simplest species, Psaronius Renaulti, 
the stem contains a single solenostele. This is presumably the most 
primitive form of the order (38). The other species are dictyostelic 
and polycyclic, each circle of strands acting as a compensation 
system to the one immediately outside, and thus eventually repairing 
the leaf-gap. Some species also possess peripheral steles; these 
anastomose with the other steles, but do not contribute to the 
formation of leaf-traces. The traces of adventitious roots are given 
off from them. Since these peripheral steles appear to be absent 
from the geologically older forms with distichous phyllotaxy, they 
are probably a later development of the more modified stems (32). 
There seems no reason to assume a close affinity between such 
strikingly different forms as the Psaronieae on the one hand and the 
Botryopterideae, Hymenophyllaceae and Gleicheniaceae on the other. 
In the Matonineae we meet for the first time the polycycly so 
characteristic of most Psaronieae. But Matonia, though polycyclic, 
is not dictyostelic. This fact, and the peculiar branching of its 
frond, appear to forbid a close affinity between the two orders. 
Many of the older botanists believed the Psaronieae and 
Cyatheaceae to be closely allied. More recently this has generally 
been denied (42), (38). But Rudolph, who has recently reinvesti¬ 
gated the Psaronieae very fully, would derive the Cyatheaceae from 
them. He regards the recent Tree Ferns as a series showing stelar 
reduction, this reduction being greatest in the simplest forms, but 
