30 BOTANY part i 



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

 the case of the Poppy (Papaver somniferum) and of the different species 

 of Bupleurum, the leaf-base surrounds or clasps the stem, the leaves are 

 described as perfoliate. If the bases of two opposite leaves have 

 grown together, as in the Honeysuckle (Lonicera Gaprifolium), they are 

 said to be connate. Where the blade of the leaf continues downwards 

 along the stem, as in the winged stems of the common Mullein (Ver- 

 bascum thapsiforme), the leaves are distinguished as decorrent. 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 instance, with many of the 

 Leguminosae (Fig. 213). The leaf-blade, in turn, may be either sharply 

 marked off from the petiole, or it may be prolonged 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 indentations ; otherwise, if only slightly 

 indented, it is usually described as serrate, dentate, crenate, un- 

 dulate, sinuate, or incised, as the case may be. When the inci- 

 sions are deeper, but do not extend more than half-way to the 

 middle of the leaf-blade, a leaf is distinguished as lobed or CLEFT 

 according to the character of the incisions, whether more or less 

 rounded or sharp ; if the incisions are still deeper the leaf is said 

 to be partite, 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; in all other cases it is said to 

 be simple. The single, separate divisions of a compound 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. The leaflets are either 

 sessile or stalked ; and sometimes also, as in Robinia and Mimosa, their 

 stalklets articulate with the spindle by means of swollen pulvini. The 

 term pedate is applied to leaves on which segments are further 

 divided on one side only, and the new segments are similarly 

 divided. Variations in the outline of leaves, whether they are 

 entire, serrate, dentate, crenate, incised, etc., as well as peculiarities 

 in their shape and segmentation, are of use in the determination 

 of plants. The venation or nervature of leaves is also taken 

 into consideration, and leaves are in this respect described according 

 to the direction of their so-called veins or _ nerves, as parallel 

 veined or netted veined. In parallel venation the veins or nerves 

 run either approximately parallel with each other or in curves con- 

 verging at the base and apex of the leaf (Fig. 31, s) ; in netted veined 



