i PHYSIOLOGY OF THE COCO-NUT 5 



with a deep water table, and the surface should not be 

 too dry. The surface should be cultivated, to prevent 

 deep drying ; but it must not be cultivated deeply 

 enough to destroy many roots, or to keep them from 

 occupying a level as near the surface as will let them 

 find a reasonable amount of water. 



Before the absorption of water is taken up, a little 

 more should be said about the structure of the roots. 

 The tip of each root is protected by a thimble-shaped 

 structure called the root-cap, which saves the growing 

 point from injury as- it is pushed through the soil. 

 The length of the cap is somewhat greater than the 

 diameter of the root. The young part of the root 

 immediately behind the cap is covered by a very 

 delicate epidermis ; it is through this that the root 

 absorbs water and the mineral food dissolved in the 

 water. The coco-nut has no root-hairs. 



The hypodermis has already been mentioned. It 

 is formed from a layer several cells thick, just inside 

 the epidermis. The cells are very small, and at first 

 have very thin walls. They afterwards thicken, and 

 soon become so thick and hard that water cannot pass 

 through them. Only the short zone between the root- 

 cap and the place where the walls of the hypodermis 

 thicken can absorb water. The larger the root, the 

 longer this zone is likely to be. In very active 

 roots it is 5 centimetres from the tip back to the 

 beginning of the hypodermis. In less active but by 

 no means inert roots, 7\ millimetres in diameter, this 

 distance may be only 2 centimetres. When the growth 

 of the roots is checked by dryness, or by any other 

 unfavourable condition of the soil, the hypodermis is 

 formed closer and closer to the tip, finally even under 

 the back part of the cap, leaving no actively absorbing 

 zone at all. 



Altogether, with its short absorbing region and the 

 absence of root-hairs, and even of really fine roots, the 

 coco - nut must be said to have a root system ill 

 adapted to the absorption of large quantities of water. 



