Affinities of Helmi n thostachys zeylanica . 433 
strand, differs entirely from it in the fact that the xylem 
is exarch as in the majority of the other species of Sela- 
ginella. Again, the fact need not be lost sight of that 
mesarchy seems to have prevailed extensively in those fossil- 
genera which have been grouped together under the name 
of Cycadofilices ; and moreover it is tolerably characteristic 
of many Leptosporangiate Ferns of the present day 1 . The 
occurrence, however, of the same mesarch character in Hel- 
minthostachys , on the one hand and in Phylloglossnm , which 
is almost generally admitted to be a primitive Lycopod, on 
the other, may possibly indicate something more than a mere 
coincidence. Amongst the Ophioglosseae, Helm in thostachys 
may be regarded as possessing some claims to be regarded as 
a representative of an old stock : for quite apart from the wide 
geographical distribution of the monotypic genus, it is, in 
respect of the stipular character of its leaves, in reality simpler 
than Ophioglossum , and perhaps even than Botrychium also. 
It is however not very easy to estimate the weight to be 
attached to this feature when the dorsiventral habit of the 
plant is borne in mind. 
The metaxylem consists of tracheids with characteristic 
bordered pits of an oval or even almost circular form, but 
other elements also occur in which the pits assimilate to the 
more scalariform type met with in other members of the 
family. The Ophioglosseae show amongst themselves some 
considerable deviation from the more regular scalariform type 
met with in the majority of Ferns, but so far as we are aware, 
Helminthostachys goes considerably beyond them in this 
character ; and it may be worth while recalling the fact that, 
judging from the fossil remains, it resembles in this respect 
many of the extinct Vascular Cryptogams, e.g. some of the 
Cycadofilices. Of course no argument is here drawn from 
this, either as to a possible relationship of the groups just 
mentioned to each other, or to Helminthostachys itself, but 
it seems worth while recalling the evident fact that this 
1 Mr. Seward has kindly drawn our attention to the fact that Lygodium , amongst 
the true Ferns, possesses exarch xylem in the stem. 
