24 
CHOICE BRITISH FERNS. 
for small collections wliere space is very limited. Most of 
tlie species have afforded examples of this, coupled with other 
types of variation. 
Congestion characterises many forms, and consists in a more 
or less crowded and overlapping state of all the divisions, 
and since it usually, though not always, involves shortening 
of the stalks as well, generally accompanies dwarfing, and 
hence is classed with it. 
Depauperation is a common form of variation, and is rarely 
regular enough in its effect to be beautiful. It is curious 
in its way, thoroughly healthy and vigorous plants constantly 
producing fronds on which the tips or some of the pinna3 
are either altogether missing, irregular in length, or very 
ragged and imperfect, exactly as if devoured by insects. These 
oddities are, nevertheless, truly transmitted, in most cases, 
by the spores. 
Variegation. — This is very rare, and we believe there have 
been found no regular variegated forms, such as some of 
the exotic species have produced, e.g., Pteris cretica albo- 
lineata and others. Some forms of the divided Ferns have 
been found irregularly splashed with white ; and yellow 
Hartstongues are not rare in collections. 
The above form the main types of variation, and two or 
more of them may be, and frequently are, conjoined in one 
and the same plant, which, of course, immensely increases 
the scope. Besides these, there are endless forms which can 
only be classed as oddities, such as the cornute and truncate 
forms, where the frond is cut short, as it were, the midrib 
projecting suddenly from the face or back of the frond, like 
a thorn ; or the frond ends abruptly in a pocket, or horn, or 
frill, or all these combined; serpentine forms, where all the 
parts, and the whole Fern itself, are lengthened, and twisted 
about like a serpent — striving, as it were, to become a climb- 
ing plant, like some of its foreign relations ; marginate 
forms, where lines or ridges run along the upper or lower 
surface, parallel with the edges or midrib ; revolute forms, 
where the frond is rolled up longitudinally, like a tube, the 
divisions taking a half-circle curve backwards ; caudate 
