10 THE LEAVES. 



principal descriptions of lease or term of life in plants. Those 

 which live for only a few months, say from spring to autumn, 

 and are then cut down by the frost, or die of exhaustion, are 

 called Annuals ; those which live, as regards their roots, for portions 

 of two years, are called Biennials ; and those which survive for a long 

 series of years, their roots retaining vitality, whether the stems die 

 down in the winter or not, are called Perennials. The turnip is a 

 biennial ; yellow lupines and sweet peas are only annuals. Plants 

 that die down in the autumn, whether annual, biennial, or peren- 

 nial, and all that are of a soft and succulent nature, whatever may 

 be their stature, are called "herbaceous;" perennials with woody 

 stems, many of the latter generally rising side by side from the root, 

 are called " shrubs ; " tall and woody perennials, with a single stem 

 from the ground, are " trees." Most stems, it should be added, 

 consist of wood, bark, and a thread of pith in the middle, like the 

 marrow in a bone. But these three elements are not always dis- 

 tinguishable, and in one large class the distinction does not exist. 

 They are best seen by cutting the branch of a tree across, so as to get 

 a horizontal section of the respective parts. Pine and fir-trees 

 shew the nature of bark very well, and young stems of elder the 

 nature of pith. Grasses and plants of the Parsley-family often have 

 hollow stems. Lastly, there is a large class of plants in which stems 

 are never developed. These arc called " stemless." 



THE LEAVES. 



No part of the plant, not even the flower, requires more careful 

 consideration than the Leaf. The source of a great part of the beauty 

 of the world, as we feel so powerfully when the verdure of Spring 

 returns, there is scarcely anything in nature more diversified, or 

 which presents forms of greater symmetry, or of more elegant sim- 

 plicity. Usually the leaf consists of a flat and thin portion called the 

 blade or " lamina," and a stalk called the " petiole." In this state it 

 is termed "petioled" or " petiolate." (Fig. 8.) But it often happens 

 that the petiole is not developed, and that the blade grows directly 

 from the stem ; it is then said to be " sessile," literally "sitting close." 

 (Fig. 7.) and if so intensely sessile as to embrace the stem, " clasp- 

 ing," or " amplexicaulent." Such leaves often have projecting 

 extremities at the base, called "auricles," or "little ears;" and there 

 are cases where the projecting parts meet upon the opposite side of 

 the stem, and grow together by their edges, making it appear as if 



