. Elementary botany . Botany. i6 FOLIAGE-LEAVES (iii.), BLADE or LAMINA. The blades of foliage-leaves exhibit great diversities of form and size. In form the lamina is usually a flat expanded plate or ribbon-like structure ; but it exhibits all variations from the narrow needle of the Scotch Pine to the circular disk of TropcRolum. Its apex may be drawn out into a fine point or end bluntly, or even terminate in an indentation. The margin is even (entire) or uneven (toothed, saw-like, scalloped, etc.). Venation of the Lamina.— The substance of the blade is traversed by veins or nerves which fre
. Elementary botany . Botany. i6 FOLIAGE-LEAVES (iii.), BLADE or LAMINA. The blades of foliage-leaves exhibit great diversities of form and size. In form the lamina is usually a flat expanded plate or ribbon-like structure ; but it exhibits all variations from the narrow needle of the Scotch Pine to the circular disk of TropcRolum. Its apex may be drawn out into a fine point or end bluntly, or even terminate in an indentation. The margin is even (entire) or uneven (toothed, saw-like, scalloped, etc.). Venation of the Lamina.— The substance of the blade is traversed by veins or nerves which frequently stand out more or less prominently. The arrangement of the veins may be grouped under two general headings—(i.) paral- lel-veining; (ii.) net-like vein- ing. In parallel-veiaed leaves a number of veins, approxi- mately equal in size, run side by side from the base of the lamina towards its tip. The veins are more or less parallel, and are connected by a limited number of smaller ones which join them at right angles. This type of venation is characteristic of Grasses, Lilies, and most other Monocotyledons. In net-veined leaves the finer veins are numerous, and form a complicated network (fig. i8). Most Dicotyledons have net-veined leaves. There are two sub-types of net-like venation—pinnate and palmate veining. A lamina which is pinnately-veined (feather-veined) has a single main vein—the mid-rib — which traverses the centre of the blade, running from the base towards the apex; this mid-rib gives off from its two sides smaller veins, which are arranged much like the pinnse of a feather— Hazel (fig. i8). Pear, Primrose. A palmately-veined leaf, in place of possessing a. Fig. i8.—Venation of Hazel leaf. (After Dennert.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Groom, Percy, 186
Size: 1386px × 1803px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1898
