176 THE LEAVES. 



persistent, when they remain through the cold season, or other 

 interval during which vegetation is interrupted, and until after the 

 appearance of new leaves, so that the stem is never leafless ; as 

 in Evergreens. 



309. Leaves last for a single year only in many Evergreens, as 

 well as in deciduous-leaved plants; the old leaves falling soon 

 after those of the ensuing season are expanded, or, if they remain 

 longer, ceasing to bear any active part in the economy of the veg- 

 etable, and soon losing their vitality altogether. In Pines and 

 Firs, however, as in many other evergreen trees and shrubs, al- 

 though there is an annual fall of leaves while the growth of the 

 season is taking place, yet these were the produce of some season 

 earlier than the last ; and the branches are continually clothed 

 with the foliage of from two to five, or even eight or ten succes- 

 sive years. On the other hand, it is seldom that all the leaves of 

 an herb endure through the whole growing season, but the earlier 

 foliage near the base of the stem perishes and falls, while fresh 

 leaves are still appearing at the summit. In our deciduous trees 

 and shrubs, however, the leaves of the season are mostly de- 

 veloped within a short period, and they all perish nearly at the 

 same time. They are not destroyed by frost, as is commonly 

 supposed ; for they begin to languish, and often assume their au- 

 tumnal tints (as happens with the Red Maple especially), or even 

 fall, before the earlier frosts ; and when vernal vegetation is de- 

 stroyed by frost, the leaves blacken and wither, but do not fall off 

 entire, as in autumn. Some leaves are cast off, indeed, while 

 their tissues, at least at .the base of the petiole, have by no means 

 lost their vitality. Death is often rather a consequence than the 

 cause of the fall. Others die and decay on the stem without fall- 

 ing, as in Palms and most Endogens ; or else the dead leaves may 

 hang on the branches through the winter, as in the Beech and 

 some kinds of Oak, to fall when the new buds expand, the follow- 

 ing spring. We must therefore distinguish between the death and 

 the fall of the leaf. 



310. The Fall of the Leaf is owing to an organic separation, 

 through an articulation, or joint, which forms between the base of 

 the petiole and the surface of the stem on which it rests. The 

 formation of the articulation is a vital process, a kind of disintegra- 

 tion of a transverse layer of cells, which cuts off the petiole by a 

 regular line, in a perfectly uniform manner in each species, leav- 



