126 COCONUT PLANTER'S MANUAL. 



Tu ordinary practice those parts of a plant which arc above ground 

 obtain sufficient oxygen for all their requirements, but the roots of 

 plants are often seriously injured through want of a suitable supply of 

 fresh air in ;he soil. The unhealthy appearance of over-watered pot 

 plants and of crops growing in badly-drained ground is primarily due 

 to insufficient supply of oxygen to their roots. 



Ca I! HON A BSO R PTIOX 

 The leave; of plants absorb carbon from the atmosphere in the form 

 of carbon dioxide gas, the carbon being retained in the leaves while the 

 oxygen is released and passed back into the air. 



This process of carbon-fixation can only be carried on in the presence 

 of light. It ceases altogether during the night and in shady places is 

 carried on so very slowly that the amount of carbon extracted from the 

 atmosphere is often insufficient to supply the proper needs of the plant. 



Similar partial starvation due to want of light occurs among thicklv 

 planted crops and in the inner boughs of trees bearing an excess of 

 leaves, and in all cases of over-crowded plants. With an increased in- 

 tensity of light carbon-fixation increases proportionally up to a maxi- 

 mum which for most plants is not attained until they are exposed to 

 direct sunligh\ 



To Combat Drought. 

 In common with every other form of life the cocoanut palm demands 

 a certain amount of water to enable it to live. If the water supply is 

 entirely withheld the palm will die, whilst if the supply is cut down to 

 a point below its normal requirements the palm will very soon begin to 

 show signs of distress. 



The roots are the first part of the cocoanut palm to be affected by 

 drought. 



When water is present in the soil there is at the extremity of each 

 rootlet, a space between the root cap and the hard outer covering of th? 

 root, and thiough this portion is absorbed the solutions of nitrogen 

 and mineral plant-food taken from the soil. In the largest roots thin 

 space is about two inches in length, while in the smallest it is only a 

 fraction of an inch. As the roots extends in length it is followed by 

 an equal extension of the hard hypodermis, and so the length of the 

 absorbing area in each root is kept constant. But -when the supply of 

 water in the soil is reduced the roots cease to grow in length, whilst the 

 hypodermis continues to extend towards the root cap. The absorbing 

 area is thus reduced from day by day until, if the drought continues, 

 it is entirely covered by the hypodermis and in its siate no absorption 

 whatever can take place. 



