THE BROWNING OF THE LEAVES 237 



in other years, and is taking precisely the same 

 course. Some say that the cooling of the soil is 

 the determining factor, but artificial experiments 

 in that direction have resulted not in the un- 

 pinning and the casting away of the leaves, but 

 in their shrivelling on the plant. The cutting 

 off of the sap through the decreased activities of 

 the roots is an alternative or a supplementary 

 explanation. But the branches of the sycamore 

 we cut down last week, thus effectively cutting 

 off the sap, will have withered leaves on them till 

 the middle of the winter. 



The shedding of its leaves by a deciduous tree 

 is not a mere negative, but a complex and masterly 

 process. The health of the tree is shown as much 

 by the way in which it gets rid of its leaves before 

 the winter as by the way it puts them on in spring. 

 A diseased tree often shows its disease by its 

 incapacity to get rid of its leaves in the proper 

 way. 



Let us ask what are the penalties for retaining 

 the broad leaves of the deciduous trees. The 

 first is the waste of vital force by evaporation in 

 excess of suction, when the colder weather comes. 

 Yes, or hot weather either, for we must not forget 

 that in tropical and sub-tropical countries the 

 approach of the dry season is preceded by a fall 

 of the leaf, just like that which precedes the winter 

 in our clime. A second penalty in our climate is 

 the overweighting and breaking of the branches 

 by the extra tons of snow that each tree would 



