The Encyclopaedia Britannica; .. A dictionary of arts, sciences and general literature . lled axillary. It is there that leaf-budsare usually developed. The leaf is sometimes articulatedwith the stem, and, when it falls off, a scar or cicatricularemains; at other times it is continuous with it, and thendecays, while still attached to the axis. In their early stateall leaves are continuous with the stem, and it is only intheir after growth that articulations are formed. Whenleaves fall off annually they are called decid.^ous; whenthey remain for two or more years they are persistent, andthe pla
The Encyclopaedia Britannica; .. A dictionary of arts, sciences and general literature . lled axillary. It is there that leaf-budsare usually developed. The leaf is sometimes articulatedwith the stem, and, when it falls off, a scar or cicatricularemains; at other times it is continuous with it, and thendecays, while still attached to the axis. In their early stateall leaves are continuous with the stem, and it is only intheir after growth that articulations are formed. Whenleaves fall off annually they are called decid.^ous; whenthey remain for two or more years they are persistent, andthe plant is called evergreen. The laminar portion of a leafis occasionally articulated with the petiole, as in theOrange, and a joint at times exists between the vaginal orstipulary portion and the petiole. The arrangement of the fibro-vascular system in thelamina constitutes the venation or nervation. In anordinary leaf, as that of the Ehn, there is observed a largecentral vein running from the base to the apex of the leaf,this is the midrib (fig. 100); it gives off veins laterally (jpri-. Fig. 100 Fig, 101. liG, 100—Leaf of Ulmvs effusa. Kcticulated venation; primary vems going tottie margin, which is seiTated. Leaf unequal at the base. Fig 101 —Multicostate divergent leaf of Castor-oil plant {Rictnm communis). ItIS palmately-cleft, and exhibits seven lobes at the margin. The petiole is in-serted a little above the base, and hence the leaf is called peltate or shield-Uke. mary veins), which either end in a curvature within themargin {curve-veined), as in LUac and Belladonna, or godirectly to the edge of the leaf (Jeather-veined), as in Elm(fig. 100) and Chestnut. If they are curved, then externalveins and marginal veinlets are interspersed through theparenchyma external to the curvature. There are also otherveins of less extent {costal veins) given off by the midrib,and these give origin to small veinlets. A leaf with only asingle midrib is said to be unicostate (fig. 100). In
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectencyclo, bookyear1902
