5^4 PHANEROGAMS. 



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 {petiole) and a flat blade {lamina) ; the 

 lamina is very commonly branched, i. 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. 133, p. 162). The sheathing amplexicaul base is not common in 

 Dicotyledons (but occurs in Umbelliferse) ; 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 Lamiiim amplex- 

 icaule, Dipsacus FuUomim, Lojiicera Capri/olium, 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 (Tropaeolum, Victoria regia, &c.). The power of Dicotyledons to 

 develop 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-thorns, and still more in the formation 

 of the ascidia or ' pitchers ' of Nepenthes, Cephalotus, Sarracenia. &c. 



The Venation of the foliage-leaves (with the exception of the thick leaves of 

 succulent plants) is distinguished by the numerous veins which project on the 

 under side, and by their curvilinear anastomoses by means of fibro-vascular 

 bundles running through the mesophyll itself. The mid-rib, which usually divides 

 the leaf into two symmetrical but sometimes into very unsymmetrical halves, gives 

 off lateral veins right and left ; one, two, or three strong nerves, similar to the 

 mid-rib, often springing in addition from the base of the lamina right and left 

 of the median line. The whole system of the projecting veins of a foliage-leaf 

 behaves like a monopodial branch-system developed in one plane, the interstices 

 being filled up by the green mesophyll in which lie the anastomoses combined 

 into a small-meshed network. Within the meshes still finer bundles are usually 

 formed which disappear in the mesophyll. In membranous cataphyllary and 

 hypsophyllary leaves and the perianth-leaves of the flowers the projecting veins 

 do not usually occur; the venation is more simple and more like that of Mono- 

 cotyledons\ 



The Flower'^. In the great majority of Dicotyledons the parts of the flower are 



^ [The structure of the leaf compared with that of the stem has been worked out by Casimir De 

 Candolle, Archives des Sciences, 1868; the 'Student' for the same year contains an abridged 

 translation of his paper.— Ed.] 



^ The floral diagrams given here are drawn partly from my own investigations, but chiefly from 

 the researches of Payer into the history of development, assisted by DjITs Flora of Baden. The 

 figures placed beneath the diagrams are intended to indicate the number and cohesion of the carpels 

 as well as the placentation in those plants the diagram of which is otherwise the same. 



