LEAVES. 



45 



ions, which do not again unite, as in the cryptogamons plants, 

 of which the fern is an example. Reticulate-Reined leaves are 

 divided into the feather-veined^ as the chestnut, and radiate- 

 veined^ as the maple. 



54. FoKM OF Leaves. — Leaves are simple or comjpound. A 

 simple leaf is when the lamina consists of a single j)iece. A 

 compound leaf consists of several parts, each of which is articu- 

 lated with the common petiole, in the same manner as the lat- 

 ter is connected with the stem. The parts of a compound leaf 

 are leaflets^ or folioles. The shape and outline of leaves are 

 found to depend chiefly upon the arrangement of the frame- 

 work or vascular portion. The form of leaves is expressed by 

 terms borrowed from the names of different objects ; as palr 

 matc^ hand-shaped ; digitate^ from digitus, the finger, &c. 



Of iihn-pU leaves there are as fol- Fig. 38. 



lows : a. Orbicular, or the round 

 leaf, — as in the Nasturtion (See Fig. 

 38, a) ; this is also peltate, having its 

 petiole inserted into the center of the 

 leaf, and thus resembling a shield. 

 It is radiatelj^-veined, and reticu- 

 late. 



b. Reniform (from the Latin ren, 

 the kidney), or, as it is sometimes 



called, kidney-form ; the ground-ivy {Glechoma) lias a leaf of this kind (See Fig. 

 38, 6) ; it is crenate, or has a margin with scalloped divisions ; ciliate, being fringed 

 with hairs, like eyelashes. The venation is radiate and reticulate. 



c. Cordate (from cor, the heart), or heart-shaped. Fig. 38, c, represents a cordate 

 leaf with an acuminated point, that is, acute and turned to one side ; the margin is 

 serrated, or notched Uke the teeth of a saw ; this kind of leaf may be seen in the 

 Aster cordifolium, or aster with a heart-shaped leaf. Some of the lower leaves are 

 curved backward, and then upward 



d. Ovate, obovate, i Fig. 39. 



oval ; these are terms ^^ — \ ^-^"-^^ %^v~>, ^ 



derived from the Latin /^ I /ffi^C^l /l}/^\ ^-^^i^^^/ 



o?;ifw, an egg. Suppose ^ ' M;\y /,\ A [x / jiS?>^></// 



the figure at 39, a, to 

 represent an egg ; if to 

 the broad end we add 

 a petiole, prolonging it 



into a mid-rib with some lateral divisions, we have, as at b, the representation of 

 an ovate leaf. If the petiole were placed at Yw. 40. 



the narrowest end, it would be an o6o?;a<e leaf. 

 An oval leaf (c), is when both the ends are of 

 equal breadth. When the length is much 

 greater than the breadth, the leaf is said to 

 be elliptical, as at d. In the ovate leaf, the 

 veins next the base are longest ; in the obovate 

 leaf, those at the apex are longest ; in the eUip- 

 tical leaf they are curved ; thus the outline of 

 the leaf varies according to the mode and de- 

 gree of the spreading of the veins. 



e. Lanceolate (Fig. 40, a) : this kind of leaf 

 may be seen in the peach-tree ; it is acuminate, 



54. Forms of leaves— a. Orbicular— 6. Reniform— r. Cordate— rf. Ovate— ObovaJp— Oval— Elliptical, 



