358 FALL OF 'JJIE LEAF. 



further to those plants which have a wide horizontal distribution; for example, 

 to those which grow wild or are cultivated from the lowlands at the northern 

 foot of the Alps to South Italy, and even further south, on the further side of the 

 Mediterranean. By journeying southwards, it will be seen that the beeches and 

 elms which, on the northern foot of the Alps near Vienna, lose their coloui- in 

 tlie beginning of October, are never discoloured before November on the moun- 

 tains of Madeira, and that whilst the planes already show leafless branches in the 

 North Tyrolese valleys at Innsbruck, they retain their leaves (although these are 

 turning yellow) on the mild shores of Lake Garda at the southern foot of the Alps. 

 In Palermo they are still adorned with dark-green foliage. Planes, indeed, in 

 certain instances remain green all winter in Greece, and thus far it was no myth 

 when Pliny spoke of evergreen planes. The Elder, which in the north is a deciduous 

 plant, in Poti, on the Black Sea, retains its green leaves through the whole winter. 

 In the oases of the North African deserts the Peach-tree keeps its foliage fresh 

 and green from one vegetative jjeriod to another, and while the blossom of this tree 

 in Central and South Europe unfolds on branches which have lost their foliage in 

 the previous autumn, in the oases the flowers are situated amongst the still green 

 leaves of the last pei-iod of vegetation. It may be confidently assumed that here 

 also the cause is the temperature and humidity of the ground, and that the planes 

 and peaches, whose roots at the end of autumn and winter are buried in a damp 

 and relatively warm soil, are the last to throw off their foliage. 



From all these considerations it cannot be doubted that the stripping of the 

 foliage depends upon the stoppage of transpiration, and primarily upon the dry- 

 ing-up of those sources from which the transpiring leaves derive their water. 

 Plants which denude themselves of their foliage of course lose with it much organic 

 material, for whose production they have toiled for months; but this loss will stand 

 no comparison with the advantages gained by the abscission of the leaves. In 

 reality, it is only a framework of emjDty cells — the dead envelopes of the living 

 portion of the plant — which is thrown away. The protoplasm has opportunely 

 withdrawn, the plastids which carried on their activity in the cells of the foliage 

 have migrated thence and taken up winter quarters in other sheltered parts of the 

 plant — in the stem, roots, or tubers, and have there deposited eveiything which 

 will be of use in the following year, such as starch, sugar, Szc. The empty cells 

 can thus be easily sacrificed to the common weal. The leaves fall to the ground, 

 where they decay and help to form natural mould, of which the posteritj^ of the 

 deciduous plants reap the beneflt. Since, by the formation of albuminous com- 

 pounds in the leaves, an abundance of calcium oxalate arises which is of no further 

 use to the plant, and is consequently stored up in such quantity at the end of 

 summer that it at last becomes burdensome to the plants, the throwing off" of the 

 foliage must really be regarded as a method of removing waste materials, and may 

 be compared to the excretion of waste which occurs in animals. 



Finally, it should be noted that only plants whose foliage lies flat on the groxind, 

 or whose branches and twigs are very elastic and bear needle-shaped leaves, are 



