428 
VASCULAR CRYPTOGAMS. 
and vertical stems, the internodes are usually undeveloped, and the leaves so crowded 
that no free portion of the stem remains uncovered, or only a very inconsiderable 
one ^ The leaves of Ferns are usually characterised by a circinate vernation, and 
they only unroll in the last stage of their growth ; the mid-rib and the lateral veins 
are curved from behind forwards. The forms of the leaves are among the most 
perfect in the whole vegetable kingdom ; they manifest an enormous variety in 
their outline, the lamina being usually deeply lobed, branched, or pinnate. In com- 
parison with the stem and the slender roots they are mostly very large, and some- 
times attain extraordinary dimensions, even a length of from 6 to lo feet (as in 
Pteris aquilina and Cibotiuni). They are always stalked, and continue their growth 
at the apex for a long time ; the leaf-stalks and the lower parts of the lamina are 
often completely unfolded while the apex is still growing (as in Nephrolepis). This 
apical growth is not unfrequently interrupted periodically {vide infra) ; in Lygodiwn 
Fig. 299. — Pteris aqiiilhta, a part of the uiuleiground stein with leaves and bases of the leaf-stalks (reduced about one- 
half) ; / older portion of the stem bearing the two bifurcations // and //', ss the apex of the weaker branch //; beside it the 
youngest leaf-rudiment 8 ; 1-7 the leaves of this br'anch, one being developed in each year ; 1-5 the leaves of earlier years, which 
have already died off at some distance from the stem ; 6 the leaf of the present year with unfolded lamina, the stalk having been 
cut off; 7 the young leaf for next year ; at the apex of the stalk is the lamina still very small and entirely clothed with hairs. The 
leaf-stalk / bears a bud III a, which has developed a leaf that has already died off. The more slender filaments are roots. M\ 
the parts shown in the figure are subterranean. 
the leaf-stalk or the rachis resembles a twining stem with long-continued growth, the 
pinnae presenting the appearance of leaves. The amount of metamorphosis of the 
leaves is, notwithstanding, very inconsiderable ; on the same plant the same forms 
of leaves, mostly foliage-leaves, are constantly repeated ; scale-like leaves occur on 
underground stolons {e.g. in Siruihiopieris germanica), and in many cases the fertile 
leaves (those which bear sporangia) assume special forms. Such differences as 
occur in most Phanerogams are not found in the development of the leaves of one 
plant; Platycerium alcicorne must, however, be mentioned, as having the foliage- 
leaves alternately developed as broad plates closely applied to the supporting surface 
and as long dichotomously branched ribbon-shaped erect leaves. 
Among the various forms of trichomes of Ferns those termed Ramenta are 
^ From the change of form and of size presented by the older cicatrices Brongniart concluded 
that the stems of the Tree-ferns continue to grow in length (and in thickness?) for some time after 
the leaves have fallen off. 
