FERNS. 



347 



Pteris aqiiilina, Cibotium, and Angiopteris). 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 Lygodium the leaf-stalk or the rachis even resembles a twining stem 

 growing for a long period, 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 (^. g. in Struthiopieris 

 geniiatiica), 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 ; Platyceriwn alcicome 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 



tIG. 359. — Pteris aqiiilitta, a part of the under^rouiKj stem witli leaves and bases of the leaf-stalks (reduced about one-half) ; 

 / older portion of the stem bearinjj the two bifurcations // and //', ss the apex of the weaker branch // ; beside it the 

 youngest leaf-rudiment 8 ; 1-7 the leaves of this branch, 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 beencut 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 II a, which has developed a leaf b that has already died off. The more slender filaments are 

 roots. All the parts shown in the figure are underground. 



erect leaves. Amons^ the various forms of trichomes of Ferns those termed PalecB 

 are especially striking, from their great numbers and from being frequently flat and 

 leaf-like ; the younger leaves are generally entirely covered and concealed by them. 



After these preliminary particulars, we may now turn to a consideradon of the 

 mode of growth of the separate organs. 



The growing end of the stem sometimes far outruns the point of attachment of 

 the youngest leaves, and then appears naked, as in Polypodium vulgare, P. sporodo- 

 carpitm, and other creeping Ferns, as well as in Pteris aquilina, where, according to 

 Hofmeister, it frequently attains in old plants a length of several inches without 

 bearing leaves. Mettenius states that in many Hymenophyllaceae leafless prolon- 

 gadons of the axis of this kind have been taken for roots. In other cases, on the 

 contrary, especially in Ferns with an erect growth, the increase in length of the 

 stem is much slower, its apex remaining enclosed in a leaf-bud. The stem generally 

 ends in a flat apex ; sometimes, as in Pteris, it is even imbedded in a funnel-shaped 



