CHAPTER VII 



THE FOLIAGE 



LEAVES are formed at the apex of the twigs of the tree in 

 such manner that the youngest leaves on the twigs are 

 always those nearest the apex. The chief function of leaves is 

 to absorb carbonic acid gas from the atmosphere. Carbon and 

 oxygen in this gas is worked up with hydrogen and oxygen, 

 found in the water sent from the roots to the leaves, to form 

 sugars and starches. This process, which is called carbon 

 assimilation, can only take place in sunlight. Every tree, 

 therefore, endeavours so to arrange its leaves that they will 

 catch the maximum amount of light. As the leaves are re- 

 sponsible for the carbon assimilation of plants, the more 

 luxuriant the foliage is the greater is its capacity for manu- 

 facturing food for the tree. Without abundant foliage the 

 growth of a tree is necessarily much hindered. The mistake 

 of close-planting is thus obvious. A poor spread of foliage is 

 inevitably the consequence of close-planting. 



As stated, it is by the leaves of plants and trees that the 

 carbonic acid gas is absorbed by the air and worked into 

 carbon compounds, and they discharge part of the constituent 

 oxygen of the gas into the air, and retain the constituent 

 carbon of the gas in their tissues. The rapidity with which 

 plants do this has been illustrated by a French scientist, 

 Boussingault. He took the growing branches of an oleander 

 plant and enclosed them in a glass vessel, and through the 

 vessel passed a current of air, which was subjected to careful 

 analysis both before and after its passage through the vessel. 

 By measuring the leaves and analysing the air passing over 

 them he found that, under exposure to sunlight, there was an 

 absorption of carbonic acid from the air at the rate of 56^ cubic 

 inches per hour, or a fixation of carbon at the rate of n-J grains 

 per square yard of leaf surface exposed, thus proving the ex- 



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