LEAF-FOKMS. 



49 



(5) BIPINNATE (twice pinnate], when the leaflets 

 themselves are pinnate, as in the Honey - Locust, 

 fig. 8; and 



(6) TRIPINNATE (three times pinnate), when the 

 leaflets are bipinnate, so that the leaf is thrice com- 

 pounded, as in fig. 5, which represents only one leaf. 



280. When a leaf consists of several finger-like divi- 

 sions, it is called Digitate, as in the Horse-Chestnut, 

 fig. 3. 



281. A TERNATE LEAF consists of three leaflets, 

 which crown the stem in a kind of whorl, as in the Clover, 

 fig. 2. At fig. 13 is a ternate leaf of the Wood-Sorrel, 

 whose leaflets are obcordate, or reversed heart-shape. A 

 Ternate Leaf is 



(1) BITERNATE, when the leaflets are themselves 

 ternate, fig. 9 ; and 



(2) TRITERNATE, when the leaflets are biternate, 

 fig. 10. 



282. A Leaf is DECOMPOUND, when it combines the 

 characters of the two principal types of the Compound 

 Leaf; and it is said to be PINKATELY DECOMPOUND, or 

 TERNATELY DECOMPOUND, as it approaches more nearly 

 one or the other of these forms. The leaf of Meadow 

 Rue, fig. 11, is Ternately Decompound. 



LEAF-MARGIN. 



283. THE MARGIN OF THE LEAF is generally marked 

 by notches of various forms. The different modes of 

 being cut present characters so uniform, as to be of con- 

 siderable importance in the distinction of species. A 

 Leaf is 



(1) ENTIRE, when there are no notches, or teeth of any 

 kind, as in fig. 1, Plate XV. The Victoria Regia, fig. 15, 

 has a remarkable leaf. It is entire, and the margin is 

 surrounded by a deep rim. It spreads out on the water 

 like a great platter, often six or seven feet in diam- 

 eter; 



(2) SERRATE, with notches like the teeth of a saw, 

 all pointing to the summit, as in figs. 2 and 3. At fig. 

 6 the leaf is biserrate, or doubly serrate ; 



(3) DENTATE (toothed), with irregular and diverging 

 notches, as in the Plane and Chestnut, figs. 4 and 5 ; 



(4) REPAND, with the margin slightly concave, 

 % 7; 



(5) CRENATE, with rounded notches, as in the Penny- 

 wort and Mallow, figs. 8 and 9 ; 



(6) LACINIATE (torn), cut in deep and irregular 

 gashes, as in Aconite, fig. 10; 



(7) INCISED (cut), the margins divided by deep in- 

 cisions, as in Crowfoot, fig. 11. Between the two last 

 there are no absolute distinctions ; the terms cut , gashed 

 and torn, being used almost, if not quite indifferently, 

 and merely represent slight variations of the lobed 

 leaf; 



(8) DISSECTED, with the parenchyma greatly deficient, 

 and barely covering the veins, so as to give the appear- 

 ance of a skeleton, as in the Water Ranunculus, fig. 13, 

 Submerged leaves most commonly take this form. In 

 the Water-Chestnut, which has already been referred to, 

 the dissected leaves near the base grow under water ; 

 while those that float on the surface are simple and un- 

 divided. The foliage of this plant is exquisitely delicate 

 and beautiful ; 



(9) FRILLED, the margin greatly expanded, as in the 

 High Mallow, fig. 1 4 ; 



(10) SPINESCENT, the notches invested with thorn- 

 like processes, as in the Holly, fig. 12; and 



(11) EROSE, appearing as if gnawed or bitten by 

 animals, as in fig. 16. 



LEAF-SUMMIT. 



284. THE APEX OF THE LEAF is also marked by 

 several variations, which are of considerable importance) 

 in specific distinctions. A leaf is 



(1) ACUTE, when it ends in a sharp point, as in the 

 Peach, fig. 1, Plate XVI. ; 



(2) OBTUSE, when it is blunt at the apex, fig. 2 ; 



(3) ACUMINATE, with a greatly attenuated point, 

 more or less curved, like a shoemaker's awl, as in figs* 7 

 and 8; 



(4) MUCRONATE, ending in a bristly point, fig. 3 ; 



(5) RETUSE, with a rounded notch at the end, fig. 4 ; 



(6) EMARGINATE, with a small, sharp notch at the 

 end, fig. 5 ; and 



(7) TRUNCATE, appearing as if cut off square at the 

 end, as in the Tulip-tree, fig. 6. At fig. 9 is a flowering 

 branch of the same beautiful tree, showing more perfectly 

 the peculiar form and venation of its fine leaves (285). 

 At fig. 10 one of the Locust tribe is seen, with its leaflets 

 arranged in opposite pairs, like delicately plumed wings, 

 and retuse at the apex. In the Lentil of the sacred 

 Scriptures, fig. 11, the leaf terminates in a tendril ; while 

 in fig. 13, the very acute, and also acuminate, leaf of the 

 Wild Radish (Raphanus) is seen. The Frond, a peculiar 

 form of the leaf, is shown in the Fern and Moss, figs. 1 4 

 and 15, and the Thallus in the Lichen, fig. 12. 



When twice pinnate. Three times. Leaf in finger-liko divisions. Three 

 divisions. Varieties of the Ternate leaf. Decompound leaf. Leaf-margin, 



varieties. Instances of each. Leaf-summit, varieties. Tulip Tree. Locust 

 Lentil. Wild Radish. Frond, in what plants? Thallus, In what ? 



