SECT. I 



MORPHOLOGY 



Sessile leaves usually clasp the stem by a broad base. Where, as in the 

 case of the Poppy (Papaver somniferum), the leaf-base surrounds the stem, the 

 leaves are described as AMPLEXICAUL ; if, as in species of Bupleurum, it com- 

 pletely surrounds the stem, the term PEHFOT.I.VTK is used. If the bases of two 

 opposite leaves are united, as in 

 the Honeysuckle (Louicera Capri- 

 folium), they are said to be CON- 

 NATE. Where the blade of the 

 leaf continues downwards along the 

 stem, as in the winged stems of 

 the common Mullein (ferbaseum 

 fhapsiforme), the leaves are dis- 

 tinguished as DECURRENT. The 

 petiole of a leaf merges either 

 directly into the leaf-base, or it 

 swells at its lower end into a 

 LEAF -CUSHION Or PULVINUS, and 



is thus articulated with the leaf- 

 base. This is the case, for in- 

 stance, with many of the Legu- 

 minosae. The leaf-blade, in turn, 

 may be either sharply marked oH' 

 from the petiole, or it may be pro- 

 longed so that the petiole appears 

 winged, or again it may expand 

 at its junction with the petiole into 

 ear-like lobes. A leaf is said to 

 be ENTIRE if the margin of the 

 leaf-blade is wholly free from in- 

 dentations, or if the latter are very 

 shallow. When the incisions are 

 deeper, but do not extend half-way 

 to the middle of the leaf-blade, 

 a leaf is distinguished as LOBKD ; 

 when they reach more than half- 

 way, as CLEFT (Fig. 35 sb) ; if the 

 incisions are still deeper the leaf 

 is said to be PARTITE (Fig. 38 I), 

 and if they penetrate to the midrib 

 or base of the leaf- blade it is termed 

 DIVIDED. The divisions of the leaf- 

 blade are said to be PINNATE or 

 PALMATE, according as the incisions 

 run towards the midrib or towards 

 the base of the leaf-blade. Where the divisions of the leaf-blade are distinct and 

 have a separate insertion on the common leaf-stalk or on the midrib, then termed 

 the SPINDLE or RHACHIS, a leaf is spoken of as COMPOUND (Fig. 35 ub) ; in all 

 other cases it is said to be SIMPLE. The single, separate divisions of a com- 

 pound leaf are called leaflets. These leaflets, in turn, may be entire, or may be 

 divided and undergo the same segmentation as single leaves. In this way double 

 and triple compound leaves may be formed. Simply and doubly PINNATE leaves 

 in which the leaflets are attached to the two sides of the rhachis are of common 



D 



Kio. 34. Lily of th Valley (Convallariu mcjalis). ntl, 

 Scale leaves ; Ib, foliage leaves ; hb, bracts ; 6, flower ; 

 i'.-.-.-, rhizome ; aw, adventitious roots. (Somewhat re- 

 duced.) 



