20 ELEMENTS OF BOTANY. 



etc. When tlie incisions are carried still deeper, the term parted is used ; 

 and when they extend to the mid-vein or base of the blade, the leaf is said 

 to be divided. 



In general outHne leaves present a multiplicity of forms, which are, 

 however, sufficiently characterized in non-technical language. Such terms- 

 as linear, lanceolate, oblong, elliptical, oval, ovoid, and orbicular are often 

 employed, and require no explanation. Oblanceolate signifies a general 

 lance-shape, but somewhat widened toward the apex, like a lance with its 

 point turned downward ; obovate, an ovate form also with its wider por- 

 tion toward the apex ; spatulate, hke a sj^atula ; cnneate, wedge-shaped, ta- 

 pering from above downward. 



Then, too, the base and apex present a variety of forms. The base 

 may be cordate or heart-shaped, reniform or kidney-shaped, auriculate 

 or eared, sagittate or arrow-shaped, hastate or halberd-shaped, peltate or 

 shield-shaped. 



The apex may be acuminate or taper-pointed ; acute when ending with 

 an acute angle and not tapering ; obtuse, blunt ; truncate, aj^pearing as if 

 cut off ; retuse, slightly notched at the extremity ; emarginate, more deeply 

 notched or indented ; obcordate, inversely heart-shaped ; cuspidate, armed 

 with a small cusp or tooth ; mucronate, armed with a very small sharp 

 point ; or aristate, with a bristle-like point. 



Thus far we have considered the leaf in its simplest form — that is, when 

 consisting of a single blade, however deeply it may be cut or divided. 

 All such leaves are termed simple (Fig. 29), in contradistinction with 

 compound leaves (Fig. 30), which are made up of two or more, often 

 many blades, supported by a common petiole. Yet this distinction of 

 leaves into simple and compound is, to some extent, arbitrary, for in leaves, 

 which are parted — that is, divided to the base or mid-vein — the lobes be- 

 come as essentially separate blades as if they were supported upon sepa- 

 rate petioles : still, such leaves are commonly considered simple. Some 

 writers simplify the matter by drawing the line at an articulation with the 

 petiole, considering those only compound which are so articulated and all 

 others simple. By articulation is meant the joint at which the leaf sepa- 

 rates when it falls from the stem. But even this division is not com- 

 j)letely satisfactory, for there are leaves — for example, the lemon— con- 

 sisting of a single entire blade which is articulated Avith its petiole, and 

 hence would under this definition have to be considered a compound leaf. 



A compound leaf, then, is made up of two or more blades, termed leaf- 

 lets (Fig. 30), borne xipon a common petiole, with which they may or may 

 not be articulated. 



Compound leaves are of two principal forms, the pinnate, in which 

 the leaflets are arranged like the pinnate veins of a simi^le feather-veined 

 leaf, and the palmate, in which they are arranged palmately. 



Pinnately compound leaves are equally pinnate when they have 



