104 



FALL OF THE LEAF 



[CH. 



evergreens, after two or three or more years, the leaf falls 

 (Fig. 57). Now this falling of the leaf is as truly a regular 



Fig. 57. Fall of leaves of the Horse-chestnut in autumn. Each 

 leaflet disarticulates from the common leaf-stalk, and the place on the 

 stem where the latter was articulated remains as a scar, as in Fig. 18 (K). 



biological phenomenon as any other phase of the plant's 

 life, and is as carefully prepared for as is, for instance, the 

 formation of a bud. 



Just before the fall of the leaf a plate of tissue is 

 formed across the base of the leaf-stalk when it is inserted 

 on the shoot. This plate of tissue is shown in section at 

 Ab in Figure 58, and it will be seen that it runs right 

 across the leaf-stalk, traversing the vascular strands (st') 

 just above the line indicated by the letters Ab. Under- 

 neath the epidermis (e, e) a layer of cork-tissue (p, p) has 

 been formed, and this affords a better protection to the 



