Il] SIMPLE LEAF 17 



The distinction between compound and simple leaves 

 is only of value on account of the enormous variety of 

 leaves to be described, and is somewhat arbitrary, the 

 whole matter really turning on the branching of the leaf. 



The leaves are compound in 



Clematis Mahonia Horse-chestnut 



Ailanthus Virginian Creeper Robinia 



Laburnum Blackberry Roses 



Dewberry Sweet-briar Raspberry 



Rowan Elder Service Tree 



Ash Walnut. 



In certain other cases, such as the Barberry, Broom, Gorse, 

 and Whin, close observation is needed to determine the 

 compound nature of the small or altered leaves. 



In the rest of the trees and shrubs to be considered 

 the leaves are simple. 



The typical simple leaf, then, commonly exhibits a 

 blade or lamina, and a stalk or petiole, and is said to be 

 petiolate (Fig. 5). In some cases, however, the petiole 

 is absent, and the lamina is sessile on the leaf-insertion, 

 as in many species of Hypericum and Honeysuckle, and 

 in the Juniper ; such sessile leaves are, however, rare 

 in our trees and shrubs. According to the expanse of 

 the insertion, and the consequent partial or complete 

 surrounding of the axis by the mesophyll, or softer green 

 tissue of the leaf, the following cases are distinguishable : . 



The particular case where opposite leaves are joined 

 at their bases, so that the stem appears to pierce them, is 

 termed connate, as in Lonicera Caprifolium (Fig. 54); 

 and other similar examples are afforded by Ghlora per- 

 foliata, a herbaceous plant not uncommon in the fields. 



When the petiole is present it may be long or short, 

 stout or slender, cylindrical, or not : very often it is 



w. ii. 2 



