430 VASCULAR CRYPTOGAMS. 



The phyllotaxis of Ferns sometimes corresponds to the rectilinear arrangement 

 of the segments of the apical cell. Thus the distichous arrangement of the leaves 

 of Pteris aqutlina, Niphobolus rupesiris, and of some species of Polypodium, corre- 

 sponds to the biseriate segmentation of the apical cell of the stem. But where the 

 phyllotaxis is complicated and spiral, and the apical cell a three-sided pyramid, as 

 occurs in Aspidium Filtx-mas, the same processes may take place as in those Mosses 

 which have their leaves arranged in many rows with a trilateral apical cell, such 

 as Polytrichum ^ 



The Terminal Branching of the stem is considered by Hofmeister to be 

 dichotomous in all Ferns '^. The branches arise very near the end of the stem, and 

 are, at least at first, equivalent to the primary stem, so that the branching is a 

 bifurcation. That the branches are independent of the leaves is inferred by this 

 writer from the fact that the ends of the stem of Pteris aquilifia, which are leafless 

 and often several inches long, regularly bifurcate. These branches are, in this 

 and in many other cases, not axillary ; and where, in other Ferns, they appear 

 axillary, we must assume, with Hofmeister, that the bifurcation has taken place 

 immediately in front of a youngest leaf, and that the limb of the fork which stands 

 before the leaf developes to a smaller, while the other (the prolongation of the primary 

 stem) does so to a greater extent. The branching at the end of the stem does not 

 necessarily take place in the same plane as the insertion of the leaf immediately pre- 

 ceding ; when it does, the branch stands laterally on the stem beside the leaf. To this 

 class belongs, according to Mettenius's description, the extra-axillary branching of those 

 Hymenophyllacese which have their leaves in two rows. That which distinguishes 

 Ferns from Phanerogams with axillary branching, especially Angiosperms, is the 

 rarity of terminal branching. While in the latter every leaf-axil, at least in the 

 vegetative region, bears a bud, even the apparently axillary branches of creeping 

 Ferns with long internodes occur mostly only at great distances, being wanting in 

 a number of intermediate leaves. In those Ferns where the growth of the stem is 

 slow and the apical region of considerable size, especially in erect species like Aspi- 

 dium Filix-mas and the Tree-ferns, terminal branching of the stem is reduced to 

 a minimum, or is entirely absent, or occurs only in abnormal cases. 



The formation of new shoots from the bases of leaf-stalks must be distinguished 

 from the normal terminal branching of the stem. These have nothing to do 

 genetically with the stem, any more than the formation of adventitious shoots from 

 the lamina of the leaves {ii)ide infra). 



The Development of the Leaf^ is exclusively basifugal and apical, the further 

 growth being also basifugal. The leaf-stalk is first formed; at its apex the lamina 

 begins subsequently to show itself; its lowest parts are formed first, its higher parts 

 in basifugal succession. The extraordinary slowness of this growth is very re- 



^ See Hofmeister, AUgemeine Morphologie, p. 509; and Bot. Zeitg. 1870, p. 441. 



^ [According to Mettenius (^Ueb. Seitenknospen bei Farnen, Abhdl. d. kgl. sachs. Ges. d. Wiss. 

 V. 1861, this is not the case. Mettenius' view has been recently confirmed by Prantl, who has 

 found that the branching in many Ferns, such as Cyitopteris montana, Phegopteris vulgaris, Dryopteris 

 calcarea, is effected by lateral buds (Flora, 1875). Ceratopleris appears to be the only Fern which 

 does not produce them (Kny, loc. cit.)] 



2 [See Sadebeck, Ueb, d. Entwick. d. Farnblattes ; Verhandl. d. bot. Ver. d. prov. Branden- 

 burg, 1874.] 



