The Phylogeny & Inter-relationship of Pteridophyta. 93 
THE PHYLOGENY AND INTER-RELATIONSHIPS OF 
THE PTERIDOPHYTA. 
A Critical Resume. 
By Lady Isabel Browne. 
Introductory. 
f )HE object of the present series of articles is to place before 
the botanical student a critical, though brief, account of the 
principal views now held as to the phylogeny and affinities of the 
Vascular Cryptogams. During the last few years there has 
accumulated a great wealth of facts and theories concerning the 
fossil and recent Pteridophytesand their connection with one another, 
but no comprehensive review dealing critically with these facts and 
theories has yet appeared. It is therefore proposed to consider 
successively the inter-relationship of the various types composing 
each phylum or main division of the Vascular Cryptogams, and the 
affinities of the phyla to one another. 
I.—SPHENOPHYLLALES. 
It will be convenient to begin this resume by a comparison 
from the phylogenetic point of view of the different members of 
fossil Sphenophyllales. These forms had an exarch cauline stele, 
which was triarch, hexarch or dodecarch ; the leaves were nearly 
always some multiple of three ; such numbers as eight, recorded by 
Mr. Seward (10) in Sphenophyllum emarginatum being exceptional 
and possibly due to imperfect preservation. Simple, and repeatedly 
dichotomous, leaves occur, sometimes on the same stem. Professor 
Lignier (7) has suggested that the simple leaves are the ultimate 
segments of a smaller number of dichotomous ones, and that the 
primitive number of these compound leaves was three. The 
following quotation will best explain his view of the Sphenophyllaceous 
leaf : “ Thisleaf alwaysshowsatleasttwoseparate lobes., which 
are usually erroneously considered each torepresent aleaf . But 
it also happens that the lobing may be greater, and being moreover 
very deep, separates from one another over the surface of the stem 
a larger number of segments, each of which simulates an 
independent leaf; these segments may, according to the case in 
