230 BUDS AND STIPULES 



posited the waste products of the chemical life-processes, 

 to be got rid of when the leaf falls or the bark peels. 

 A leaf which has served its time and then been dropped 

 contains quantities of calcium oxalate, resinous and 

 gummy matter, and, like the bark also, alkaloids, such 

 as nicotin, them, and other nitrogenous excreta. 



Climate has, naturally, a great influence on the 

 length of time during which leaves remain attached. 

 Where autumn is prolonged the leaves also last long. 

 Thus, for the neighbourhood of Naples, excepting when 

 winter sets in unusually early, Tenore quotes the end of 

 November for the leaf-fall of the Walnut, Ash, Lime, 

 Oak, and Poplar, and states that the leaves of the Apple, 

 Beech, Elm, and Birch often last till the end of De- 

 cember, and the Cherry is evergreen. Foliage generally 

 will keep longer in a damp, sheltered spot than in dry, 

 sunny, exposed positions, and longer after a wet than a 

 dry summer. Trees do not lose their leaves at the same 

 time : not only are Oaks and Elms still green when the 

 Horse Chestnuts and Limes are almost bare, but some 

 individual trees retain their leaves longer than others of 

 the same species. Apart from conditions of climate or 

 weather, each species has its own peculiarity in this 

 regard. This may sometimes be due to the fact that 

 species now growing together in one country have come 

 originally from somewhat different climates. A plant 

 may have contracted the habit through long generations 

 of shedding its leaves early or late, as the case maybe, and 



