172 THE LEAVES. 



Sect. III. The Duration of Leaves, and the Geneeal 

 Action of Foliage. 



307. Leaves last only for a limited period, and are thrown off, 

 or else perish and decay on the stem, after having fulfilled their 

 office for a certain time. 



308. Duration of leaves. In view of their duration, leaves are 

 called fugacioits, when they fall off soon after their appearance ; 

 deciduous, when they last only for a single season ; and persist- 

 ent, when they remain through the cold season, or other interval 

 during which vegetation is interrupted, and until after the appear- 

 ance of new leaves, so that the stem is never leafless ; as in Ever- 

 greens. 



309. Leaves last only for a single year 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 vegetable, 

 and soon losing their vitality altogether. In Pines and Firs, how- 

 ever, although there is an annual fall of leaves either in autumn or 

 spring, 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, successive years. On the 

 other hand, it is seldom that all the leaves of an herb endure 

 through the whole growing season, the earlier foliage near the base 

 of the stem perishing while fresh leaves are still appearing above. 

 In our deciduous trees and shrubs, however, the leaves of the 

 season are mostly developed 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 autumnal tints (as happens with the Red Maple 

 especially), or even fall, before the earlier frosts ; and when vernal 

 vegetation is destroyed by frost, the leaves blacken and wither, but 

 do not fall off entire, as they do in autumn. Some leaves are cast 

 off, indeed, wliile their tissues have by no means lost their vital- 

 ity. Death is often rather a consequence than the cause of the 

 fall. Others die and decay on the stem without falling, as in 

 Palms and most Endogens. In some cases many of the dead 

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

 falling only when the new buds expand, the following spring. We 



