BOTANY. 1§! 



when those at the apex are longest. Leaves also are cuneate or wedge- 

 shaped {fig. 8) spathiilate {fig. 9), subulate {fig. 10) ; acuminate, or drawn 

 out into a point of greater or less extent {ftg. 11); niucronate, with the free 

 extremity of the midrib projecting from the margin {fig. 12). 



When the parenchyma is deficient at the apex, so as to form two rounded 

 lobes, the leaf is obcordate ; when the deficiency is very slight, it is 

 emarginate ; when the apex is merely flattened or slightly indented, the 

 leaf is retuse {fig. 13). If the apex appear as if cut off, so that the margin 

 is straight or obtusely angled, the leaf is truncate {fig. 14). A leaf is 

 cordate when the petiole enters a base having a rounded emarginatioii 

 [fig. 15), and kidney-shaped or reniform when the apex also is rounded 

 {fig. 16). When the lobes are prolonged downwards and acutely, the leaf 

 is sagittate {fig. 17) ; hastate, when they proceed at right angles. When 

 the veins of leaves spread out in more than one plane, and by the develop- 

 ment of parenchyma a succulent leaf is produced, we may have conical, 

 ensiforni or sword-like, prismatic, acinacifoi'm or scymoter-shaped {fig. 18), 

 and dolabriform, or axe-shaped leaves {fig. 19). The margin of the leaf 

 may be wai'ij, undulated, or crisped, Avhen it is puckered from a superabun- 

 dance of cellular tissue. There are numerous other shapes of leaves, 

 although these and their binary combinations are the most important ; the 

 rest will readily suggest themselves. 



Compound leaves are leaves in Avhich the divisions pass down to the 

 midrib, so as to subdivide the leaf into smaller and distinct leaves, called 

 leaflets. The midrib or petiole thus appears like a branch with so many 

 distinct leaves, each articulated to it. When the compound leaf dies, it is 

 generally the primary petiole that fiills off, carrying with it all those 

 secondary to it. Leaflets, like leaves, may be either sessile or supported on a 

 distinct stem, called a petiolule. 



A feather-veined compound leaf is said to be pinnate {fig. 20) when each 

 one of the primary veins forms the midrib of a leaflet : bipinnate {fig. 21) 

 when the secondary veins are midribs, and are articulated to the primary ; 

 tripinnate or decompound when the tertiary veins stand in the same relation 

 to distinct leaflets : a leaf still further divided is supradecompound. 



When a pinnate leaf has one pair of leaflets, it is wiijugate ; two. 

 bijugatc ; many pairs, mnltijvgatp. When a pinnate leaf ends in a pair of 

 pinnae, it is equally or abruptly pinnate {pari-jyinnate) : a single terminal 

 leaflet furnishes an unequally pinnate {i?npari -pinnate) leaf. When the 

 leaflets are not directly opposite to each other, the leaf is alternately 

 pinnate : it is inipari-pinnate when the pinnae are of unequal size. 



In leaves with radiating venation, and in which each vein forms the 

 midrib of a separate leaflet, we have a tennate leaf with three leaflets ; 

 quaternate with four ; quinate with five, (fcc. Should the parenchyma 

 connecting three ribs of a ternate leaf subdivide, so that each of these forms 

 the midrib of a new leaflet, the compound leaf is biternate ; another such 

 subdivision gives a tr item ate leaf, <fcc. • 



The petiole, or that part of the leaf which unites the blade with the stem, 

 consists of one or more bundles of vascular tissue, with a varying amount 



19 



