640 PHANEROGAMS. 



the leaf where the principal veins radiate '. On the adventitious buds on the leaves 

 of Utricularia, Pringsheim's treatise already quoted may be consulted. Adventitious 

 buds more often spring from roots, e.g. in Anemone japonica, Linaria vulgaris ^ 

 Cirsium arvense^ and Populus tremula, according to Irmisch^. The shoots which 

 spring from the bark of the older stems of trees must not at once be set down as 

 the development of adventitious buds ; since the numerous dormant buds of woody 

 plants may long remain buried and yet retain their vitality. 



The Leaves of Dicotyledons exhibit a greater variety both in their position and 

 their form than those of all other classes of plants put together. The ordinary 

 phyllotaxis of seedlings begins with a whorl of two cotyledons, and continues 

 either in decussate pairs or passes into a distichous arrangement or into whorls 

 consisting of larger numbers or spiral arrangements with the most various angles 

 of divergence. More simple arrangements, especially that of decussate pairs, are 

 generally constant in whole families, the more complicated arrangements usually less 

 constant. Axillary branches usually begin with a pair of leaves which are either 

 opposite or alternate, and stand right and left of the median line of the mother-leaf. 



It is quite impossible to give in a short space even a general account of the 

 forms of leaves, even apart from cataphyllary leaves (scales on underground 

 stems and those which envelope persistent buds), hypsophyllary leaves or bracts, 

 and floral leaves; only a few of those forms of foliage-leaves can be mentioned 

 here which are peculiar to or characteristic of Dicotyledons. The foliage leaves 

 are usually divided into a slender leaf-stalk {peliole) and a flat blade {lamina) ; the 

 lamina is very commonly branched, /, e. lobed, pinnate, compound, or incised ; and 

 even where it forms a single plate (simple leaf) the tendency to branching is gene- 

 rally indicated by indentations, teeth, or incisions in the margin. The branching 

 of the lamina has usually a distinctly monopodial origin, but its development may 

 continue in a cymose manner, a helicoid succession of lateral lobes being formed 

 on each side right and left of the centre of the leaf (as in Rubus, Helleborus, 

 &c., see Fig. 141). The sheathing amplexicaul base is not common in Dicotyledons 

 (but occurs in Umbelliferae) ; and the occurrence of Stipules in its place is more 

 common. The cohesion of opposite leaves into a single plate pierced by the stem 

 is not uncommon (' perfoliate ' leaves, as in Lamium amplexicaule, Dipsacus Fullonum, 

 Lonicera Caprifolium, species of Silphium, Eucalyptus, &c.) ; as well as the downward 

 prolongation of the lamina of the leaves (' decurrent leaves '), which distinguishes the 

 ' winged ' stem of Verbascum, Onopordon, &c. The not uncommon ' peltate ' leaf also 

 scarcely occurs in so marked a manner in any other class {TropcBolum, Victoria regia, 

 &c.). The power of Dicotyledons to develope from their foliage-leaves organs of 

 the most diverse functions adapted to the most various conditions of life is seen in 

 a very striking manner in the common occurrence of leaf-tendrils and leaf-spines, 

 and still more in the formation of the ascidia or ' pitchers ' of Nepenthes, Cephalotus, 

 Sarracenia, &c. 



Saxifraga granulata, Detitaria bulbifera, Rafmncidus Ficaria, &c. [Berge, Ueb. Bryophyllnm calycimim, 

 Zurich 1877.] 



* The common method of propagating Begonias is by cutting or tearing the leaf, which, if then 

 placed on moist soil, produces buds on the edges.] 



^ [Irmisch, Bot. Gaz. III. pp. 146 and 160.] 



