1 62 
Notes . 
adult stems of many Ferns the solenostelic structure (specially pre- 
dominant in the middle grade — Prof. Bowers Gradatae — of the Fern 
series) is phylogenetically transitional between the protostelic structure 
almost certainly primitive for the Ferns, and the dialystelic condition 
characteristic of the great majority of the higher forms (Polypodiaceae). 
The young plant of these higher forms (in certain cases at least) starts 
by laying down the protostelic structure, but very soon this gives 
place to the solenostelic, which in its turn passes into the dialystelic 
arrangement characteristic of the adult stem. The great interest of 
the Lindsay a-iy^o, of stele is that it appears to furnish a phylogenetic 
link hitherto wanting in a mature stem (see Boodle, Anatomy of 
Schizaeaceae, p. 407, Ann. of Bot., XV, 1901) between the protostelic 
and the solenostelic structure ; and this view is distinctly supported by 
the occurrence of the same type at the same stage in the ontogenetic 
series of the Ferns already mentioned. 
The chief objection to this hypothesis of the morphological position 
of the Lindsaya - stele is the fact that the Lindsayeae are relatively 
advanced Ferns so far as their sori are concerned, coming into Prof. 
Bower's highest grade, the Mixtae, with a flat receptacle, no definite 
order of development among the sporangia, and a nearly if not 
quite vertical annulus. The great majority of the rest of the 
Mixtae (Polypodiaceae in the wide sense) have dialystelic structure. 
There is, however, evidence that the Lindsay a-type is not wanting 
among the more immediate allies, of the Lindsayeae, the Davallieae, 
while the Dennstaedtiaceae, which appear to come immediately below 
in the series, are predominantly solenostelic ; whether they will supply 
evidence of similar transitions we do not as yet know. It is not to 
be supposed that all the morphological characters of the Ferns will 
evolve strictly pari passu, and if an anatomical character of a relatively 
low grade is well adapted to general conditions of habit and the 
like, there is nothing surprising in its being retained in plants in 
which evolution of the sorus has advanced considerably. This, 
however, is a large question, which we hope to treat more fully in our 
detailed paper. We may expect also a considerable elucidation of 
the whole of these relations as a result of Mr. Gwynne-Vaughan's 
extended researches on the solenostele, the second instalment of which, 
dealing with the Cyatheaceae in the wide sense, and the Davallieae, 
we may hope to see published within the next few months. 
Meanwhile we may point out that there are not wanting 
