ELEMENTS OF STRUCTURAL BOTANY. 



73 



leaves, the Beecli, Mullein, and Willow supply familiar 



instances. The Mallow, Maple, 

 Grape, Currant, and Gooseberry 

 have simple radiate- veined leaves. 

 Sweet-Brier (Fig. 43), Mountain- 

 Ash, and Rose have comijound 

 pinnate leaves, whilst those of 

 Fig. 109 Vii-ginia-Creeper (Fig. 109), 



Horse-Chestnut, and Hemp are 



compouncl digitate. 



As has already been pointed out, the leaves of Mono- 

 cotyledonous plants are almost invariably straight- 

 veined. 



103. In addition to the venation, the description of 

 a simple leaf includes particulars concerning. (1) 

 the general outline, (2) the edge or margin, (3) 

 the point or apex, (4) the base 



104. Outline. As to outline, it will be convenient 

 to consider first the forms assumed by leaves without 

 lobes, and whose margins are therefore more or less 

 continuous. Such leaves are of three sorts, viz : those 

 in which both ends of the leaf are alike, those in which 

 the apex is narrower than the base, and those in which 

 the apex is broader than the base. 



105. In the first of these three classes, it is evident 

 that any variation in tlie outline will depend altogether 

 on the relation between the length and the breadth of 

 the leaf. When the leaf is extremely narrow in com- 

 parison with its length, as in the Pine, it is adcz^ar 

 or uecdlcshaped (Fig. 110). As the width increases, 

 we pass through the forms known as linear, ohlowj, cvr-l, 

 and finally orhicvlar, in which the width and length 

 are nearly, or quite equal (Fig. 111). 



