ORGANS OF NUTRITION. 



135 



Fig. 257. 



2. INSERTION, AND ARRANGEMENT OF LEAVES. 



1. Insertion. — The point by which a leaf is attached to the 

 stem is called its insertion. Leaves are inserted on various parts 

 of the stem and branches, and receive dilFerent names accord- 

 ingly. Thus the first leaves which are developed are called 

 cotyledons, nursing, or seminal; the latter term however is a 

 bad one, because it would indicate that these are the only leaves 

 that exist in the seed, but this is not the case, as the gemmiile 

 or plumule also possesses rudimentary ones; the cotyledons are 

 usually very different in their appearance from the ordinary 

 leaves which succeed them. The first leaves which appear after 

 the cotyledons are termed primojdial. These, and the cotyledons, 

 generally perish as soon as, or shortly after the development of 

 the other ordinary leaves. The latter are 

 called radical, when they arise at, or be- 

 low the surface of the ground, and thus 

 apparently from the root, but really 

 from a shortened stem, or crown of the 

 root as it is commonly called. Leaves 

 are thus situated in what are termed 

 acaulescent plants, as in many Violets, 

 the Dandelion, Primrose, Plantain, &c. 

 The leaves which arise from the main 

 stem are called cauline ; those from the 

 branches ramal; and those from the base -^'s;- 

 of, or upon the flower- stalks, ^ora/ leaves 

 or bracts. 



When a leaf arises from the stem by means of a stalk it is 

 said to be stalked or petiolate {fig. 255); when the blade of a leaf 

 is fixed to the stalk by a point more or 

 less within its margin, as in the Indian 

 Cress {fig. 257), and Castor Oil, it is 

 peltate or shield-shaped; when the stalk 

 is absent, so that the blade arises di- 

 rectly from the stem, it is said to be sessile 

 {fig. 263); when a leaf is enlarged at its 

 base and clasps tlie stem from which it 

 springs, it is amplexicaul or embracing, as 

 in Fool's Parsley, &c. {fig. 258), or if it 

 forms a complete sheath around it, as in 

 Grasses generally {figs. 259 and 351, ^) it 

 is said to be sheathing; when a leaf is pro- 

 longed as it were from its base, so as to 

 form a winged or leafy appendage down 

 the stem, as in Thistles, it is decurrent {fig. 

 260); when the two sides of the base of 

 a leaf project beyond the stem and unite 

 {fig. 261), as in the Hare's-ear {Bupleu- 

 K 4 



Peltate leaf of 

 fhe Indian Cress {Ti-o- 

 pceolum). 



Fig. 258. Amplexicaul 

 petiole of Angelica. 



