172 



MORPHOLOGY OF MEMBERS. 



transformed into the sporogonium, a structure without leaves, roots, or branches, 

 the sole function of which is the production of spores. A new Moss-plant is, 

 on the contrary, constituted by the production of a leaf-bearing shoot from 

 a branch of the alga-like Protonema, which branches, strikes root (by root- 

 hairs), and is independently nourished. The shoot first produced, from which 

 are developed the rest, is termed the Primary Shoot ; it is often more strongly 

 developed than its lateral shoots, as in most Ferns, Cycadeae, Coniferae, Palms, 

 and Amentiferae. The primary shoot produces Lateral Shoots of the first order 

 or Secondary Shoots, these again lateral shoots of the second order, and so on. 

 Nevertheless it often happens that lateral shoots of any order take root and 



become detached from the primary shoot; 

 they then assume all its peculiarities, and 

 may equally be considered as primary 

 shoots. But it also happens that the 

 primary shoot itself is arrested at an 

 early period, while new orders of shoots 

 proceed from it which gradually become 

 more vigorous, as in many bulbous and 

 tuberous plants. Shoots which become 

 detached from the mother-plant when but 

 slightly developed, continue to grow by 

 independent nourishment, and repeat the 

 peculiarities of the primary shoot, are 

 called GemmcB or Bulbils ; they are often 

 adventitious shoots; but bulbils may also 

 be shoots of normal origin, as in many 

 species o^ Allium. 



Fig. i^T.—Asplenitan decussatum ; middle part of a 

 mature leaf; its mid-rib st bears the pinnae / /; at the base 

 of one of these is formed the bud K, which has also already 

 put out a root (natural size). 



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-bearing shoots. 



(a) In many Ferns leafy shoots arise from Lewves, and especially when the stem 

 branches but little or not at all, as in Nephrodium Filix-mas, Asplenium Filix-fcRmina, 

 Pteris aquilina, &c. In these species the buds spring singly out of the lower parts of the 

 petiole at a greater or less height above its insertion. In other species it is usually 

 the lamina which produces numerous buds, generally in the axils of the pinnae, as in 

 Asplenium decussatum (Fig. 127), A. Bellangeri, A. caudatum, Ceratopteris thalictroides, or 

 on the surface of the leaf itself, as in Asplenium furcatum, &c. In all these cases the 

 buds produced on the leaves are exogenous in their origin, and those on the petioles 

 of the first-named species arise, while the leaves are still very young, out of single 

 superficial cells ^ These shoots take root while still in connexion with the mother-leaf, 

 but sooner or later become detached ; in Nephrodium Filix-mas and Pteris aquilina often 

 only after some years, when they have already acquired considerable strength, and the 

 base of the mother-leaf has died off and decayed. 



In Phanerogams buds also occur on leaves, although much more rarely. The best 



^ Hoftneister, Beitrage zur Kenntniss der Gefass-Kryptogamen, vol. II. Leipzig 1857. 



