FILICIDE A E. IIOMOSPOR US FILIC1NEA E. 



209 



The leaves of the Ferns are generally distinguished by their circinate arrangement 

 in the bud ; the mid-rib and the lateral veins are rolled up from behind forwards, and 

 only unroll when the growth is just being completed. The forms of the leaves are 

 among the most perfect in the vegetable kingdom ; they show a marvellous variety in 

 the general outline, and the lamina is usually repeatedly lobed, branched and feathered. 

 They are generally very large in proportion to the stem and the slender roots, 

 reaching sometimes extraordinary dimensions ; those of Ptcris aquilina, Cibotium and 

 Angiopteris may be from ten to twenty feet in length. They are always stalked and 

 continue to grow at the apex for a long time ; the stalk and the lower parts of the 

 lamina are often fully unfolded when the apex is still growing, as in Nephrolepis, and 

 this apical growth of the leaf is in many cases interrupted periodically, a point which 

 will be noticed again below ; in Lygodium the leaf-stalk or the mid-rib may even 

 become like a climbing stem with long-continued growth, on which the pinnae appear 

 as leaves. At the same time the metamorphosis of the leaves is slight and unim- 

 portant ; the same forms, and these chiefly f<51iage-leaves, are continually repeated on 

 the same plant ; scale-like leaves are found on subterranean stolons in Struthiopteris 

 germanica and Osmunda regalis, where as in Cycadeae and other plants they alternate 

 with the foliage-leaves and envelope the bud at the apex of the stem in winter 



FIG. 156. A portion of the underground stem of Pteris aquilina. with leaves and bases of leaf-stalks, half the 

 natural size. / older portion of the stem, bearing the two bifurcations // and //' ; ss the apex of the weaker branch //. 

 close to it the youngest leaf-rudiment s ; i 7 the leaves of this branch, one of which is developed in each year ; i 5 the 

 leaves of earlier years, which are already dead to a certain distance from the stem, 6 the leaf of the present year with 

 unfolded lamina and with the stalk cut through, 7 the young leaf for the next year with its lamina still quite small and 

 covered up with hairs at the apex of the stem. The leaf-stalk i bears a bud /// a which after developing a leaf that is 

 already dead has now become dormant. The more slender filaments are roots. All the parts shown in the figure are 

 subterranean. 



(Prantl). In many cases the fertile leaves, those which bear sporangia, assume 

 special forms ; but the great amount of variation in the development of the leaves of 

 the plant, which occurs in the Phanerogams, is not found in the Ferns; yet Platycerium 

 aldcorne must not be forgotten, in which the foliage-leaves alternate periodically as 

 broad sheaths closely pressed against the surface on which they grow, and as long 

 ribbon-like erect dichotomously branching leaves, which are however generally sterile 

 in our hot-houses. Of the different forms of hair-structures in the Ferns the most 

 remarkable for their number and flat leaf-like appearance are the ramenia (chaff-scales 

 or paleae), by which the younger leaves are usually covered and concealed. 



After these preliminary remarks we may now proceed to the consideration of the 

 growth of the several members. 



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