,8,,. THE FALLING OF LEA VES. 689 



epochs, those which were the first to leaf were also the earliest to 

 lose their leaves. A chestnut in the garden of the Tuileries, from its 

 habit of early leafing, is known as the \'ingt Mars, and ]\I. Henri 

 Vilmorin states that, compared with the other chestnuts in the gardens, 

 it keeps its leaves beyond the mean timeot leaf-fall. M. Vilmorin also 

 observed thirty-four horse-chestnuts 150 years old in a plantation on 

 his own property at Verrieres in 1876 and 1877. He found that those 

 which were the first to lose their leaves in 1876 were again in the 

 same category next year, with slight differences as to order. Six of 

 those which were the first to put out leaves in spring were late to lose 

 them in autumn, while five others were early in leaf and early in losing 

 leaf. He concludes that the two phenomena have no regular relation. 

 A tree which is a precocious leafer in the spring may either be early 

 or late in shedding its foliage in the autumn. He found, however, that 

 in the majority of cases lime trees {Tilia platyphylla) which were early 

 to leaf were late in losing leaf. Observations on the beech and elm, 

 the latter at Geneva, showed, as in the case of the chestnut, no 

 relation between the two phenomena. 



In conclusion, we may notice how plants utilise the fact of their 

 leaves being merely temporary structures. Leaves share with the bark 

 (also transient) the functions of the excretory organs of an animal ; 

 in their cells the plant deposits those by-products and residues 

 from the chemical life-processes of which it can make no further use, 

 and which are thus got rid of when the leaf falls. A leaf which has 

 run out its full time and then been dropped, will contain quantities of 

 calcium oxalate, resinous and gummy matter, and often alkaloids, 

 such as nicotine, thein, and others, which form the nitrogenous 

 excreta of plants. On the other hand, useful matter like starch, 

 sugar, and proteid has been gradually removed and passed back to 

 the stem. 



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1. Duhamel du Monceau. — La Physique des arbreb. Paris; 1758, vol. i, p. 129. 



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