Prof. Vaucher on the Fall of Leaves. 335 



tary be broken on all sides, and irregularly, as the peduncles 

 of a great many species of fruit ; and a tree deprived of its 

 leaves would present branches loaded with useless vestiges of 

 their former footstalks — a species of disorder which is never 

 seen in Nature. 



In examining more closely the phenomena of the fall of 

 leaves, it is observed that their separation is favoured by the 

 torsion of the peduncle. This torsion is seen in leaves which 

 are ready to drop off, and in those which have fallen. M. 

 Vaucher observed it in the apple, the peach, the cherry, the 

 willow, and many other trees, but did not notice whether it 

 followed the same direction in all. The ring or circle which 

 indicates the approaching fall is most easily perceived on the 

 approach of autumn. It is double in the orange, the leaves 

 of which sometimes break off by the first mark, sometimes by 

 the second. In the barberry it is placed above the point of 

 contact between the leaf and the stem, so that, after the fall of 

 the leaf, the rudiments of the leaf-stalk may protect the young 

 bud. 



In compound leaves, while the parenchyma retains its func- 

 tions, the adherence between the two systems of fibres or ves- 

 sels is maintained ; but when the leaf has finished its growth, it 

 twists and dries by little and little, the fibres and the vessels are 

 disunited, and the least exterior agitation breaks the adhesion. 

 In this case, however, the separation is not so determinate as 

 in simple leaves. Sometimes the entire leaf separates itself 

 from the stem, and the leaflets remain adherent ; sometimes 

 portions of the common leaf-stalk break off — often leaflets ; 

 and never, as may be easily conceived, does this rupture (de- 

 termined by the drying up of the parenchyma alone) appear 

 so clean and well-defined as in simple leaves. Traces, more 

 or less distinct, of the disorganized parenchyma are often to 

 be observed adhering at the place of separation. 



It is not difficult to reconcile what is here said with the 

 phenomena which the fall of leaves presents. Since the rup- 

 ture of the leaf-stalk depends upon a primitive organization, 

 and the period of its fall is determined by the increase of the 

 stem, and the branches of the year begin to harden at their 

 ha.se, it is easy to understand why the inferior leaves are detach- 



