





22 THE BRITISH FERNS. 
and Ferns which have their fructification in this position are called 
Dorsiferous. Most of the British Ferns are dorsiferous. When 
the fructification is protruded from the edge of the frond, it is said 
to be extra-marginal. In the extra-marginal fruited group the 
spore-cases are often collected around the free extremities of the 
veins, which are surrounded by thin urn-like expansions of the 
cellular tissue, as in Trichomanes and Hymenophyllum. In Osmunda 
the marginal spore-cases are quite exposed. 
The normal development of the dorsiferous Ferns is, of course, 
to bear their fructification on the under surface or back of their 
fronds, but in this dorsiferous class there are some curious deviations 
from the rule, the sori growing either above instead of beneath, or 
above as well as beneath; while in some instances those having 
their fructification normally extra-marginal, have also produced sori 
on the plane surface of the frond, both above and beneath. The first 
noted instance of this deviation from the normal state, of which 
we have any knowledge, was recorded by us* in the early part of 
1856, in the folio edition of this work. We then had occasion to 
mention that certain varieties of Scolopendrium vulgare habitually 
produce sori on the upper as well as on the under surface of their 
fronds. This occurs, for the most part, in those varieties, several 
in number, in which the margin is deeply lobed. In these cases it 
often appears as if the normally-placed sori, opposite the acute sinuses 
of the lobes, had been continued to the margin, and then returned 
on the upper surface; though in many instances the abnormally- 
placed sori are distinetly within the margin, and borne in positions 
where there are no corresponding sori beneath. Another instance 
of this abnormal position of the. sori, occurs in the Polypodium 
anomalum, subsequently recorded and figured by Sir W. J. Hooker.+ 
In this, which is a plant of polystichoid aspect, the sori are mostly 
* Moore, Ferns of Great Britain and Ireland, Nature-Printed, t. 42. 
+ Hooker, Kew Journal of Botany, viii. 360, t. 11. 

