The Death and Fall of Leaves. 319 



even the leaves are all developed within a short period, and 

 t hey ;ill 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 

 Jfcaple especially), or even fall, some weeks anterior to the 

 earliest frosts; and when vernal vegetation is destroyed by 

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

 as in autumn. Some leaves fall, perhaps, before they have 

 entirely lost their vitality. Others die and decay on the stem 

 without falling, as in Palms and most Endogens ; or else the 

 dead leaves mostly hang on the branches through the winter, 

 as in the Beach and some kinds of Oak, and fall when the new 

 buds expand, the following spring. We must therefore distin- 

 guish between the death and the fall of the leaf. 



The fall of the leaf is owing to the formation of an articula- 

 tion, or joint, between the base of the petiole and the stem on 

 which it rests. The leaf rapidly acquires its full growth, — in 

 a few weeks at farthest, — and since its base cannot long keep 

 pace with the continually increasing circumference of the stem, 

 especially as the leaf is more and more enfeebled as the sea- 

 son advances, a separation therefore takes place by the forma- 

 tion of a joint, which in our trees is well marked long before 

 frost occurs. When it falls, a well defined scar is left. But 

 in most Endogenous plants, where the leaves are scarcely, if at 

 all, articulated with the stem, which increases little in diame- 

 ter subsequently to its early growth, they are not thrown off, 

 but simply wither and decay; their dead bases or petioles 

 being often persistent for a long time. 



But why do leaves die? Why, in all ordinary cases, do 

 they only last for a single year, or a single summer ? The an- 

 swer to this question is to be found in the anatomical structure 

 of the leaf, and the nature and amount of the fluid which it 

 receives and exhales. The water which the roots absorb, dis- 

 solves, as it percolates the soil, a small portion of earthy mat- 

 ter. In limestone districts especially, it takes up a sensible 

 quantity of carbonate and sulphate of lime, and becomes 

 hard. It likewise dissolves a small proportion of silex, alumen, 

 magnesia, potassa, &c. A part of this mineral matter is depo- 

 sited in the woody tissue of the stem. But a large portion is 



