COCONUT PLANTER'S MANUAL. 35 



an important factor in the setting of tomato fruits, and that by an 

 efficient conservation of soil moisture 'blossom drop" of tomatos can 

 be reduced. 



The above, together with the fact that an increase of button fall 

 of coconuts follows a period of drought, leads to the conclusion that 

 the abscission of youngest fruits may be caused by a deficit of soil 

 moisture beyond a certain limit. That a similar cause may lead to 

 the abscission of larger grown fruits is worthy of consideration. 



Nut-fall of coconuts in Ceylon occurs principally during the rains 

 of north-east monsoon. Nut- fall therefore occurs, not when there is 

 a deficit of moisture, but during the wettest times of the year. This on 

 the face of it would appear to negative any idea that a deficit of soil 

 water is a contributory cause of nut-fall. 



The root system of the coconut palm, however, is peculiar in 

 many respects. The roots have no root hairs, and water can be absor- 

 bed only through the epidermis of a short region of the root immediately 

 behind the root tip. The remainder of the root is covered by a rigid 

 shell, called a hypodermis, which is impermeable to water. When the 

 growth of the roots is checked by dryness or other unfavourable con- 

 dition of the soil, the hypodermis is formed nearer to the tip and 

 ultimately no absorbing zone at all is left. Coconut roots are there- 

 fore ill adapted to the absorption of large quantities of water. In 

 nature, no roots will grow to any distance into water, nor into a level 

 of soil where water stands, and a rise in the water level ultimately 

 kills the submerged roots. 



The hypodermis is impermeable not only to water but also to air. 

 The roots are to a large extent dependent on special breathing organs 

 or Pneumatophores for the their air supply. These breathing organs 

 are specialised roots and their structure is such that open serial com- 

 munication is maintained through the pneumatophore to the internal 

 tissues of the parent root. Consequently the coconut requires an 

 open, well ajrated soil, and any tendency towards water-logging will 

 interfere with the air supply to the root. An excess of water in the 

 soil may therefore seriously interfere with the vital processes of the 

 roots, leading to a reduced absorption of water and ultimately to the 

 death of the roots. This in effect becomes equivalent to an actual 

 water shortage. 



Nut-fall of coconuts occurs principally in the Galagedara side of 

 the Kurunegala district, and is there most prevalent during the rains 



