20 Journal of the Asiatic Society of Bengal. [J anuary, 1915. 
(1) The cuticle of the old leaves are not so impermeable 
to water as that of young leaves.! 
increasing age. ; 
(3) ‘* Perhaps leaf activity gradually becomes impaired 
through continued accumulation of excreta and the increased 
clogging of the stomata by dust.”’* _ 
Apart from other considerations, age by itself may 
instance ? : 
Leaf-fall is considered to be induced mainly by a failure 
may be working at the same time. The resting buds may be 
stimulated into activity by the rising heat at the commence- 
ment of the hot season. Becoming active, they begin to 
develop and grow and draw the sap-current to themselves, so 
that the usual supply to the old leaves is cut off. The old 
leaves, thus suffering from physiological drought, rapidly form 
abscision layers and fall off. Schimper ° in another connection 
says: ‘*It-suggesta that). ... 6.0.0.0, the swelling buds draw 
the transpiration current to themselves.’ 
Jost says: ‘‘ correlation between the fully developed leaves 
and the rudiments of the next year’s growth prevents an 
1 Bergen, Bot. Gaz., Vol. 38, 1904. 2 Bergen, ib. 
8 Text-book of Botany, p. 567. 
4 Coulter, Barnes and Cowles, Text-book of Botany. 
ter, Barnes and Cowles, in their Text-book of Botany, p. 354, 
say: ‘*In the leaves of woody plants... . there is with age, as a rule, @ 
steady accumulation of dry matter and a rising proportion of ash.” 
§ Plant Geography. Eng. Trans., page 245. 
