PHYSIOLOGY OF THE COCO-NUT 7 



a gummy substance, and no more water is taken up by 

 it. Experiments show that, as was presumed from the 

 structure, coco-nut roots are not injured by moderately 

 strong solutions of common salts. More than this, 

 they absorb such solutions freely. They will absorb a 

 solution one hundred times as concentrated as ordinary 

 soil water about as rapidly as they do pure water. In 

 fair weather, they absorb most rapidly in the afternoon, 

 less so in the forenoon, and very slowly at night, the 

 most rapid absorption following closely the time of 

 most rapid evaporation from the leaves. This indicates 

 that the tree does not store up any considerable amount 

 of available water. And from this it follows that any- 

 thing which interferes with the evaporation from the 

 leaves immediately checks the absorption of water and 

 of mineral food by the roots. 



In proportion to the area of apparently absorbing 

 surface, the finer roots take up more water than the 

 larger ones. A calculation based on the measured 

 activity of the main roots would show that an entire 

 tree takes up at most 24 litres in a day ; but 

 we know from determination of evaporation from the 

 leaves that this figure is too low. It is likely that such 

 measurements of the growth as have been made likewise 

 fail to show how rapid it can be. The most rapid 

 growth that I was able to measure at San Eamon for 

 a period of a few days amounts to only about a metre 

 a year ; and measurements extending over a month or 

 more showed only half of this rate. More recent 

 measurements in La Laguna on eleven roots showed an 

 average growth of 3*02 millimetres a day, or somewhat 

 more than a metre a year. 



The Leaf. — The water taken up by the epidermal 

 cells of the root moves inward from cell to cell, into 

 the vessels of the axial strand. In these vessels, it 

 moves upward through the roots and trunk, to the 

 leaves, and along the midribs and veins and veinlets of 

 the leaflets. Finally, it moves outward again toward 

 the epidermis, and is evaporated. As the water 



