ORGANS OF NUTRITION. 133 



port, and which, by their ramification, form what are called 

 veins, ribs, or nerves. 



The parts of the stem from which the leaves arise, are called, 

 as we have already seen, nodes ; and the space between two 

 nodes, an internode. The part of the leaf next the stem is called 

 the base, and the opposite extremity the apex. The surfaces of the 

 leaf are sometimes called the pagince; hence, in ordinary leaves, 

 which have but two surfaces, we speak or the upper pagince, and 

 the lower. The terms upper and lower are applied to the two 

 surfaces of the leaf, because in by far the greater number of plants, 

 the leaves are placed horizontally, so that one surface looks to 

 the heavens, and the other to the earth. We shall find how- 

 ever hereafter, that there are some leaves which are placed 

 vertically, as in some Acacias, Eucalypti, &c. The lines con- 

 necting the base and apex of the leaf are called the edges or 

 margins, or collectively the circumscription. The angle formed 

 by the union of the upper surface of the leaf with the stem is 

 called the axil ; and everything which arises out of that point 

 is said to be axillary. This is the normal position, as we have 

 seen, of buds. If any body springs from the stem above, or be- 

 low the axil, it is extra-axillary; or, as generally described 

 when above, supra-axillary ; if below, infra-axillary. 



The Leaf varies as regards its duration, and i-eceives different 

 names accordingly. Thus, when it falls soon after its appear- 

 ance, it is said to be fugacious or caducous ; if it lasts through- 

 out the season in which it is developed, deciduous or annual; or 

 if beyond a single season, or until new leaves are developed, 

 so that the stem is never without leaves, it is said to be per- 

 sistent, evergreen, or perennial. 



When a leaf separates from the stem, it either does so by de- 

 caying upon it, when it is said to be non-articulated, or by an 

 articulation, in which case it is articulated. The remains of a 

 non -articulated leaf, as they decay upon the stem, are some- 

 times called reliquicb or induvios ; and the stem is said to be 

 induviate. When a leaf separates by an articulation, it leaves a 

 scar, cicatricula, or cicatrix. 



The leaf in the highest state of development, consists of three 

 distinct parts: namely, of an expanded portion, which is usually 

 more or less flattened (fig. 254, I), called the lamina, blade, 

 or litnb ; of a narrower portion, by which this is connected with 

 the stem, called the petiole or leafstalk (p) ; and of a portion 

 at the base of the petiole, or of the lamina, if that is absent, 

 which either exists in the form of a sheath or vagina ((/), en- 

 circhng the stem, or as two little leaf-like appendages on each 

 side, Avhich are called stipules {fig. 255, ss). 



These three portions are by no means always present, though 

 this is frequently the case. Thus, the leaves of the Water 

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