ORGANS OF NUTRITION. 167 



usually shorter, and broader {fig. 326), it is reniform or 

 kidney-shaped, as in the Asarabacca (Asarum eu?'opcEum); when 

 a leaf is reniform but with the lobes at the base pointed, so 

 that it resembles the form of a crescent (fig. 328), it is 

 lunate or crescent-shaped, as in Passijlora lunata. When a leaf 

 is broad and hollowed out at its base into two acute lobes, 

 and pointed at the apex, so that it resembles the head of an 

 arrow {fig. 329), \i\s sagittate or arrow-shaped, as in the Arrow- 

 head {Sagiitaria sagittifo(ia) ; Avhen the lobes of such a leaf 

 are placed liorizontally, instead of passing downwards, it is 

 hastate or halbert-shaped {fig. 330), as , in Sheep's SoiTel 

 {Rumex Acetosella) ; when the lobes of such a leaf are separated 

 from the blade, as in the upper leaves of the "Woody Night- shade 

 {Solanum Dulcamara), it is auriculate {fig. 331). When a leaf 

 is perfectly round, it is orbicular {fig. 333), a figure which is 

 scarcely or ever found, but when it approaches to orbicular as in 

 Pyrola rotundifolia, it is subrotund or rounded {fig. 332). 



It frequently happens, that a leaf does not present accurately 

 any of the above-described figures, but exhibits a combination 

 of two of them, in which case we use snch terms, as ovate-laiwe- 

 olate, linear -lanceolate, cordate-ovate, cordate-lanceolate, elliptico- 

 lanceolate, roundish-ovate, &c,, the application of which will be 

 at once evident. 



5. Form. — By this term we understand the solid configuration 

 of a leaf, that is including its length, breadth, and thickness. The 

 terms used in defining the various forms are therefore especially 

 applicable to thick, fleshy, or succulent leaves - namely, those 

 which are commonly produced Avhen the veins are developed 

 in various planes, and connected by a large development 

 of parenchyma. Such leaves either assume some regular geo- 

 metrical figures, as cylindrical, pyramidal, conical, prismatic, 8ic., 

 or approach to some well known objects, and are hence termed 

 ensiform or sword-like, acinaciform or scimitar-shaped, dolahrijorm 

 or axe-shaped, clavate or club-shaped, linguiform or tongue-shaped, 

 &c. The above terms need no further description. In other 

 instances, the leaf instead of having its veins entirely connected 

 by parenchyma, is more or less hollowed (Wt in its centre, when 

 it is said to be tubular, hood-shaped, urn-shaped, &c. ; various other 

 singular forms are also found, some of which will be hereafter 

 alluded to in speaking of the transformation of leaves. 



Besides the above-described modifications of Outline, Form, 

 Margins, &c., of simple leaves, they also present various others, 

 when we regard their surface, texture, colour, &c. For their eluci- 

 dation however we must refer to the general contents of this 

 volume. 



Compound Leaves. — We have already defined a compound 

 leaf (see p. 1 56). Its separate parts or leaflets present all the 

 modifications of margins, incision, apex, outline, form, &c., as 

 M 4 



