VARIOUS ORIGIN OF EQUIVALENT MEMBERS. 



151 



ment, while they repeat the peculiarities of the primary shoot, are called Gemmse 

 or Bulbils ; they are often adventitious shoots ; but bulbils may be shoots of normal 

 origin, as those of many species of Allium. 



Now that we have already spoken of the origin of leaves, hairs, and roots, and 

 entered sufficiently into detail on the more important points (sects. 20, 21, 22), it only 

 remains to go a little further into the various modes of origin of leaf-forming shoots. 



(a) The Formation of Leaf-forming Axes from Ihallomes (without the medium of a 

 germ-cell) occurs only in the Muscineae, especially in Mosses. From their spores, but 



VlG.iiB.—Afm'um hormon (xso); -wiv parts of root-hairs of mature plants which have put 

 out protonenia-threads n n when the sod has been inverted in damp air ; on these are formed 

 the leaf-buds A' A". 



also from the root-hairs and other parts, are developed Conferva-like segmented 

 filaments (Fig, 118, «/z) growing at the apex, and branching. These often continue to 

 grow for a long time, obtaining their nourishment independently, and sooner or later 

 produce short lateral branches, generally at 

 the base of longer branches. The apical 

 cell, in which elsewhere segmentation of 

 the filament is always produced by septa, is 

 in them divided by oblique walls, and a usu- 

 ally triangular pyramidal apical cell of the 

 stem is thus formed, the oblique segments 

 of which at once dcvelope into leaves ; and 

 thus shortly stalked leaf-buds arise (Fig. 

 118, AT AT), which at once take root by root- 

 hairs, and become developed into inde- 

 pendent Moss-stems. 



(b) In many Ferns leaf-shoots arise 

 from Lea'ves, and especially when branch- 

 ing of the stem seldom or never take place, 

 as in Aspidium Fi/ix-mas, Jlsplenium Filix- 

 foemina, Pteris aquilina, &c. In these species 

 the buds spring singly out of the lower parts 

 of the leaf-stalk at a greater or less height 

 above its insertion. In other species it is 

 the lamina which mostly produces nume- 

 rous buds, generally in the axils of the laci- 

 niae, as in Asplenium decussatum (Fig. 119), 



A, Bellangeri, A. caudatum, Ceratopteris thalictroides, or on the surface of the leaf 

 itself, as in Aspknium furcation, &c. In all these cases the buds produced on the leaves 



Fig. iig.—AsJ>lemtfm decussatum; middle part of a mature 

 leaf; its mid-rib st bears the laciniae //; at the base of one the 

 bud K is formed, which has also already put out a root 

 (natural size). 



