70 STRUCTURE OP LEAVES. 



139. A leaf, in general, whether aerial or submerged, consists of a 

 flat expanded portion (fig. 132 I), called the blade, limb, or laminar 

 menthal (fttyos, a part, and 0XAoV, a frond), of a narrower portion 

 called thepetiole (petiolus, a little foot or stalk), stalk, orpetiolary merithal 



(fig. 132 p), and sometimes of a portion 

 at the base of the petiole, which forms a 

 sheath or vagina (fig. 132 #), or is de- 

 veloped in the form of leaflets, called 

 stipules (fig. 191 s). The sheathing por- 

 tion or vagina merithal is sometimes 

 incorporated with the stem, and has 

 been called Tigellary (tige, Fr., a stem 

 or stalk), by Gaudichaud. These por- 

 tions are not always present. The 

 sheathing, or stipulary portion, is fre- 

 quently awanting, and occasionally only 

 one of the other two is developed. 

 When a leaf has a distinct stalk it is called petiolate; when it has none, 

 it is sessile (sessilis, from sedeo, I sit). When sessile leaves embrace 

 the stem, they are called amplexicaul (amplector, I embrace, and caulis, 

 a stem). The part of the leaf next the petiole or the axis is its base, 

 while the opposite extremity is the apex. The surfaces of the leaf are 

 called the pagince (pagina, a flat page), and its edges or margins form 

 the circumscription of the leaf. The leaf is usually horizontal, so that 

 the upper pagina is directed towards the heavens, and the lower pagina 

 towards the earth ; but in many cases leaves are placed vertically, as 

 in some Australian Acacias, Eucalypti, &c. ; in other instances, as ia 

 Alstromeria, the leaf becomes twisted in its course, so that what is 

 superior at one part becomes inferior at another. 



140. The upper angle formed by the leaf with the stem is called its 

 axil (axilla, arm-pit), and every thing arising at that point is called 

 axillary. It is there that leaf-buds (* 178) are usually developed. 

 The leaf is sometimes articulated with the stem, and when it falls off" 

 a scar or cicatricula remains ; at other times it is continuous with it, 

 and then decays gradually, while still attached to the axis. In their 

 early state all leaves are continuous with the stem, and it is only in 

 their after-growth that articulations are formed. When leaves fall 

 off annually, they are called deciduous; when they remain for two 

 or more years, they are evergreen. The laminar portion of a leaf is 

 occasionally articulated with the petiole, as in the Orange (fig. 185), 

 and a joint at times exists between the vaginal or stipulary portion 

 and the petiole. 



Fig. 132. Leaf of Polygonum Hydropiper, with a portion of the stem bearing it ?, Limb 

 lamina, or blade, p, Petiole or leaf-stalk, g. Sheath or vagina, embracing the stem, and ter- 

 minated by a fringe. 



