STRUCTURAL BOTANY. 45 



f SIMPLE LEAVES. 



90. In simple leaves we note their parts, tlieir consis- 

 tency, position, insertion, outline (general and partial), and 

 surface. 



1. Pakts, Consistency, Position, and Insertion of the 



Leaf. 



91. Paets of the Leaf: a, the Made or expanded 

 part, with its nerves (and their ramifications); h, 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. 



92. Consistency of Leaves. — The leaf ia either : a, car- 

 nose, fleshy ; h, membranaceous, very thin ; c, coriaceous, 

 leathery ; or d, heriaceoiis, neither too thick, nor very thin. 



93. Position of the Leaves. — Leaves are said to be : a, 

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

 the stem ; c,yfflsc4cfe(?, when they grow in clusters, as those 

 of the larch ; d, cdternate, 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; *, verticillate, in whorls; k, sparse or scat- 

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

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



94. Insertion of the Leaves. — Leaves are : a, sessile, 

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

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

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



