92 



" It must be borne in mind, too, that it is not necessary 

 that articulated leaves should be dead when they fall, as we 

 frequently find them lying upon the ground green and appa- 

 rently vigorous for a time ; and if we examine any of them 

 that have fallen naturally, we shall frequently, if not always, 

 find that the base of the petiole is plump, fresh, and appa- 

 rently living, which it would not be were its vitality entirely 

 gone. 



" The provision for the separation being once complete, it 

 requires little to effect it ; a desiccation of one side of the leaf 

 stalk, by causing an effort of torsion, will readily break through 

 the small remains of the fibro-vascular bundles ; or the in- 

 creased size of the coming leaf-bud will snap them ; or if these 

 causes are not in operation, a gust of wind, a heavy shower, 

 or even the simple weight of the lamina, will be enough to 

 disrupt the small connexions, and send the suicidal member to 

 its grave. 



" Such is the history of the fall of the leaf. We have found 

 that it is not an accidental occurrence, arising simply from 

 the vicissitudes of temperature and the like, but a regular and 

 vital process which commences with the first formation of the 

 organ, and is completed only when that is no longer useful : 

 and we cannot help admiring that wonderful provision that 

 heals the wound even before it is absolutely made, and affords 

 a covering from atmospheric changes before the part can be 

 subjected to them. 



" In the copper-beech, and some other trees whose leaves 

 die some time before they fall off, the development of the 

 starch-bearing cells on the distal side of the articulation does 

 not take place; nor is there that disruption or disintegration of 

 the cell walls which is ordinarily met with. The joint, how- 

 ever, consists of laxer tissue, which is readily broken through 

 by any accidental violence, such as winds and storms of rain, 

 or by the growth of the new leaf at the base of the petiole 

 at the commencement of spring." 



