THE 
HEW PHYTOIiOGIST. 
Vol. VII., No. 8. October 31ST, 1908. 
THE PHYLOGENY AND INTER-RELATIONSHIPS OF 
THE PTERIDOPHYTA. 
By Lady Isabel Browne. 
IV.—THE LYCOPODIALES (continued). 
SELAGINELLACE/E and Lycopodiace^e. 
Selaginella is the only existing genus of the Selaginellaceae, 
but Professor Halle’s and M. Zeiller’s recent researches have cast 
light on certain heterosporous herbaceous Palaeozoic Lycopods, 
formerly known as Lycopodites. These forms, now called Selagi- 
nellites, though only known as impressions, appear to be very close 
to Selaginella and ought probably to be included in the same order 
as the latter. Miadesmia membranacea, recently fully described by 
Miss Benson, appears to belong to the same cycle of affinity, though 
it shows certain characters peculiar to itself. 
The most primitive type of stele found in Selaginella is 
presumably the protostele of S. spinosa. The creeping axis of this 
species contains an endarch and the erect stem an exarch protostele. 
Professor Harvey Gibson, in 1894, selected S. laevigata var. Lyallii 
(a highly complex species which may, in places, possess as many as 
thirteen steles) as exhibiting the most primitive type of stelar 
anatomy and sought to derive the protostelic S. spinosa, as well as 
the other types of stele occurring in the genus, from such a type. 
At that time, however, the primitiveness of the protostele was not 
as widely accepted as at the present day ; but though most botanists 
would probably accept the primitiveness of the protostele of S. 
spinosa the case in favour of the exarch protostele being more 
primitive than the endarch one is not so clear. The complete absence 
of centripetal xylem in the creeping axis of this species is a strong 
argument against the primitiveness of exarchy. But there is good 
reason to believe that among the Ferns spiral vessels, representing 
true protoxylem, tend to disappear when the growth of the axis has, 
