

























26 THE BRITISH FERNS. 
occupies a vertical position, extending from the hinder base of the 
spore-case up the back and over to the front side, extending there 
some distance downwards. The basal part of the ring is also often 
lengthened out into the form ofa pedicel or stalk, by which the case 
is attached to the receptacle, though sometimes hardly any elonga- 
tion takes place, beyond the base of the cases, which are then sessile 
on the receptacle. The spore-case itself consists of a thin cellular 
shell, without internal divisions, traversed externally by a single: 
line of short transverse parallel thickened cells, which form the 
belt or ring. It seems to be the elasticity of this ring which. 
causes the rupture of the enclosing case, and the liberation of the 
spores, for if examined at the mature stage, especially when exposed 
to a drying atmosphere, they may be seen to burst open with a sud- 
den jerk, which scatters the spores in all directions. After this 
rupture has taken place, the spore-cases may be seen to consist of 
two hollow helmet-like portions, held together by the recurved ring, 
which looks like a jointed strap. This rupture of the spore-cases 
in the case of the vertical-ringed Ferns, takes place by an irregular 
— transverse fissure at a point on the anterior side, which M. Fée calls 
the stoma or mouth, where the striz or joints of the ring become 
dilated into elongate parallel cells, the weakening incidental to which 
elongation nó doubt facilitates disruption. The bursting of the spore- 
cases takes place with considerable force, but the two parts into which 
they become split asunder, are held together by the ring itself, which 
does not separate at that part which was opposite the stoma in the 
perfect spore-case. 
In the Trichomaninec, which includes the British genera Tricho- 
manes and Hymenophyllum, the ring of the spore-case is horizontal 
or oblique instead of vertical, and the spore-cases are vertically 
compressed. In cases where this structure occurs, the rupture or 
fissure of the ring is vertical. 
In the Osmundine the ring is reduced to a rudimentary condition, 

