388 Prof. Vaucher on the Fall of' Leaves. 



7. The temporary adhesion or solder should be found in all 

 forest trees of cold and temperate climates, of<which the leaves 

 are parenchymatous, and of a loose tissue, and which belong 

 to the class of Dicotyledons. M. Vaucher is not aware of what 

 happens in regard to trees of the torrid-zone, and is inclined 

 to suspect that Monocotyledonous and arborescent vegetables 

 enjoy not this property, or at least it may be modified in re- 

 gard to them. 



Such is Professor Vaucher's theory of the Fall of Leaves. 

 Whether he be right or not in assigning the solution of con- 

 tinuity between the leaf-stalk and the stem as the sole cause 

 of the fall, we stop not to inquire. To us it appears to be 

 only the last of a train of circumstances intended to produce 

 this effect. The pressure of the bud — the increase of the 

 stem — and the diminution of transpiration and absorption, 

 caused by change of temperature, may all be said to contx*i- 

 bute to the fall of the leaf : But M. Vaucher has the merit 

 of first directing the attention of Vegetable Physiologists to 

 an organic structure at the base of the petiole, which has 

 escaped the observation of Malpighi and Grew, as well as of 

 later writers ; and has shown that the connection of the vessels 

 of the stem and the leaf, though necessarily intimate, is mere- 

 ly temporary. A similar arrangement, there is little doubt, 

 pi-evails in the other parts of plants which successively drop 

 off — in the corolla and stamens, for instance — and in the means 

 by which the capsules or pericarps of many plants burst open 

 for the discharge of the seed ; and although this last circum- 

 stance has been marked by botanists as a specific distinction, it 

 has hitherto failed to lead to the investigation of the means by 

 which this rupture is accomplished. This investigation offers 

 a new field for botanical research, and will no doubt furnish 

 matter for future and interesting observation. 



