156 PLANT LIFE. 



a brown-green ; Maples show all sorts of rich orange, or 

 reds of one shade or another ; and "Willows become 

 white or grey. 



Just before the death of all the cells of the leaf, 

 a breaking layer and cork sheet are formed across the 

 base of the stalk. After all these preparations, the 

 slightest breath of wind carries away the leaf carcase, 

 which falls to the ground and is there promptly 

 attacked by fungi, bacteria, worms, etc. These work 

 up the dead matter of the leaf into the material for 

 new leaves, just as worn-out locomotive engines are 

 broken to pieces in the workshops to be manufactured 

 into new, and probably better designed types. 



Before closing this chapter it would be correct to 

 give some sort of estimate of the work done by foliage, 

 or of the energy which can be extracted from the 

 sun's rays by vegetation and utilised by mankind. It 

 is, however, not possible to do this with any sort of 

 reasonable accuracy. A single leaf of a sunflower or 

 pumpkin produces in a summer day of fifteen hours 

 something like twenty-five grams of starch per square 

 metre of surface (see Strasburger, Text-book, p. 201). 

 The most recent estimate of the rate at which leaves 

 work is given by Dr. Horace Brown in his address to 

 the British Association {Nature, 1899, p. 474). The 

 leaf uses up about 600,000 calories per square metre 

 of leaf surface per hour, of which a large amount is 

 employed in evaporating the water which is being 

 continually given off. The increase in dry weight 

 amounted in his experiments to about one gram per 

 square metre per hour. These results do not, however, 

 give even an approximate idea of the way in which 

 work is carried on by the sunlight. 



Animal life depends upon foliage and food manu- 



