22 
THE FERN WORLD 
though flowerless, are seed-hearing. But they do not get 
their seeds, like other plants, through the medium of flowers, 
for the curious fact is that their seeds or spores are always, 
under a very beautiful but singular arrangement, borne 
either upon the hacks or on the edges of their fronds. The 
vegetable tissue of which the fronds of Ferns are composed 
is traversed by a series of veins arranged sometimes in 
parallel lines, sometimes being forked in various ways, and at 
other times variously radiating from the bases to the edges 
of the pinna?, pinnules, or lobes. The seed-clusters are 
generally borne upon or attached to the veins at the backs 
of the fronds, although in some instances the receptacle — the 
name of that portion of the veins to which the spore cases 
are attached — is projected beyond the edge of the fronds. 
The particular form and position of these seed-clusters 
serve as a means of classifying Ferns, or enabling them to 
be grouped in accordance with a convenient arrangement. 
When they are borne upon the back of the frond they are 
usually arranged either in lines or in heaps. Sometimes 
they are arranged in a double row along each side of and 
parallel with the mid-ribs of the pinna? ; sometimes in double 
rows on each side of the mid-veins of the pinnules ; and 
sometimes they form two lines which meet at an angle on 
each pinnule, the point of union of the lines being towards 
the apex of the pinnule. In other cases they form oblique 
lines on each side of the mid-veins, the lines starting from 
near the mid-veins and proceeding outwards to the edges of 
the pinnules. Sometimes they almost completely cover the 
under-surface of the pinnules of the frond, whilst occasionally 
they are in turn themselves concealed by a dense cloud of 
scales which thickly cover them. Again, in some cases they 
are borne along the outer edges of the under-surface of the 
pinnules or of the lobes of the pinna?, and sometimes, as we 
have seen, they are projected beyond the leaf margins. 
