384 THE UNIVERSE. 



Lastly comes the stalk, composed of a stem bulging 

 at successive points; it is peculiar to the family of 



CHAPTER III. 



THE LEAF. 



To the tunic of leaves by which plants are covered is 

 due all the magnificence of creation. The flowers, indeed, 

 form a charming ornament which attracts and seduces 

 the eye, but they remain unnoticed in the grand scenes 

 of Nature, when she unrolls before us her most splendid 

 landscapes, her sombre forests, or her immense extended 

 plains of verdure. 



To the leaf is confided one of the most important 

 functions of vegetable life — respiration. Leaves then are 

 only the lungs of plants. It is seldom that they are un- 

 provided with them, yet such is the case with some 

 Euphorbife, the stem of which, inordinately swollen, en- 

 tirely replaces them, and only bears very insignificant 

 rudiments of such structures. 



The leaf is composed of two parts: the petiole or support, 

 and the blade, which is spread out in the form of a mem- 

 posed between bundles of woody and vascular tissue/, these descend from the 

 leaves, and curving inwards, pass down near the nii;ldle of the stem for some 

 distance, as shown in fig. 208, and then taking an outward course terminate at 

 the circumference. The older formations, being thus continually pressed out- 

 wards, become harder and more compact than those in the interioi-. The stems 

 of palms have no true bark, but are covered with a cortical integnment similar 

 to that of exogens. — Thompson's Gardener's Assistant. 



