STRUCTURAL BOTANY. 45 



t SIMPLE LEAVES. 



00. In sm.jjle leaves we note their parts, their consis- 

 te7icy, position., insertion, outline (general and partial), and 

 surface. 



1. Parts, Consistency, Positiox, axd Ixsektion of the 



Leaf. 



01. Pakts of the Leaf: «, the hlade or expanded 

 part, with its nerves (and their ramiiications) ; J, the 

 petiole or leaf-stalk, which is often enlarged at its base, or 

 wrapped, more or less, in the form of a sheath, around the 

 stem or branch, or closely united with the stipules. The 

 petiole is often wanting. 



02. Consistency of Leaves. — The leaf is either : a, car- 

 nose, fleshy ; h, 7nemhranaceous, very thin ; c, coriaceous, 

 leathery ; or cl, herlaceous, neither too thick, nor very thin. 



03. Position of the Leaves. — Leaves are said to be : «, 

 radical, issuing from the root ; h, cauline, springing from 

 the stem ; Cj/h^czcZtY?, when they grow in clusters, as those 

 of the larch ; d, alternate, one above the other, on nearly 

 opposite sides; e, opposite, two against each other, at the 

 same node or knot, as those of the Labiates ; f, decussate, 

 when the successive pairs of opposite leaves form a cross 

 with each other at right angles ; g, cruciate, four leaves in 

 a whorl, placed crosswise, as those of some species of bed- 

 straw ; h, distichous, in two vertical ranks, as the leaves 

 of the yew ; i, verticillate, in whorls ; k, sparse or scat- 

 tered, irregularly spiral ; I, equitant, riding astraddle, 

 when conduplicate leaves alternately embrace. (PI. II., 10.) 



04. Insertion of the Leaves. — Leaves are : ay sessile, 

 without a petiole (stalk), PI. I., 22 ; h, petiolate oy petioled, 

 with a petiole (which is sometimes channelled, or vaginate, 

 or winged). Pi. L, 13 ; c, decurrent, running down the 



