.^T. III. NATURAL DECAY. 515 



vital principle can now no longer act upon it from 

 the intervention of the dead or diseased portion of 

 the plant beyond which it has withdrawn itself. 

 But in the natural process of vegetation the neces- 

 sary change is effected by the leaf on the one hand, 

 in its yielding to the influence of physical or chemi- 

 cal agencies, and withering and shrinking into nar- 

 rower compass, when the usual supply of sap is no 

 longer transmitted to it ; and by the vital principle on 

 the other, in its controlling and directing of chemical 

 agencies so as to facilitate the final detachment of 

 the foot-stalk, and form the scar necessary to its own 

 protection. And this effect is operated by the con- 

 verting of the substance that cements the respective 

 fibres of the leaf-stalk and branch together from a 

 soft and glutinous to a dry and brittle consistence, 

 analogous to the change that takes place in the 

 seams of the valves of ripening capsules or pericarps, 

 so that the leaf falls at last merely by force of its 

 own weight, or of the slightest breath of wind, but 

 without the intervention of any previous chink o* 

 crack. 



And if it is necessary to illustrate the fall of the 

 leaf by any analogous process in the animal economy, 

 it may be compared to that of the shedding of th4 

 antlers of the stag, or of the hair or feathers of other 

 beasts or birds, which being like the leaves of 

 plants, distinct and peculiar organs, fall off and are 

 regenerated annually, but do not slough. 



ART. a. The Fall of the Flower. The flowers, 

 2 L 2 



