CASUALTIES OF VEGETABLES. CHAP. Xlf. 



But Theophrastus was himself acquainted with 

 the fact of the fall of the leaves of Evergreens, as 

 every accurate observer of nature must be, though 

 they do not actually fall till the young leaves have 

 begun to appear, so that trees of this sort are never 

 left wholly without leaves, which it was hence sup- 

 posed they never shed. In warm climates it is said 

 that many plants retain their leaves for several 

 years ; but in temperate and polar climates there 

 are no such plants to be found. 



Such is the fact of the annual fall of the leaves. 

 What is the cause of their fall ? The solution of 

 this question seems to have totally baffled the at* 

 tempts of phytologists, and to have been a puzzle 

 that no one could make out. Du Hamel, one of the 

 most sagacious and industrious of all phytologists, 

 laboured hard to explicate the phenomenon, but 

 without success. He observed that leaves which 

 fall the soonest transpire the most, and are conse- 

 quently the soonest exhausted and rendered unfit 

 for the discharge of their functions ; so that the 

 period of the fall of the leaves of different species 

 is probably in proportion to their capacity for trans- 

 piration. Their fall is accelerated by frost, or by 

 excessive heat, followed by rain. It is also acce- 

 lerated, if not actually induced, by the structure of 

 the pedicle which is very different from that of the 

 branch, having no prolongation of pith, and nothing 

 analogous in its mode of insertion, nor in its ex- 

 ternal figure, which is divisible into an upper and 



