34 THE RUBBER TREE BOOK 



in. The water is drawn through the walls of the cells and their 

 root-hairs owing to the great avidity of the cells for water, an 

 avidity largely due to greater concentration of salts. This 

 power is greater the nearer the cell is to the centre of the root. 

 The cells of the roots becoming distended with fluid, their elas- 

 ticity tends to force it out, but inwards towards other cells, 

 owing to their avidity for water. Each successive cell becomes 

 a receiving- vessel for the fluid in turn, and, being constructed 

 by the great architect of Nature upon the same principle, in 

 turn is charged and discharged. This tendency of a cell to 

 absorb moisture from one below better supplied is just as a 

 piece of sponge squeezed dry would absorb moisture from a wet 

 piece in contact with it. The quantity of water passed through 

 a plant in a comparatively short time is very large. 



To raise sufficiently-abundant supplies, the root-pressure 

 which inaugurates the work needs to be supplemented. This 

 is done in part in the leaves by means of evaporation. The 

 under sides of all leaves of trees, and to a much less extent 

 the upper sides, are full of small openings through which super- 

 fluous water is got rid of. The cells of the leaves evaporate 

 into the air between them most of the water that has brought 

 the mineral food from the roots, and this moisture finds its way 

 out through the openings. While supplies of moisture are 

 abundant, evaporation freely takes place, yet undue evapora- 

 tion is prevented during very hot, dry weather and during the 

 prevalence of drying winds. At such times the lip-like cells 

 at the openings on the under sides of the leaves, themselves 

 affected by the drying action, close in together, so narrowing 

 the openings, to prevent waste of moisture. There is no 

 suggestion that absorption of moisture for the leaf-cells may go 

 on through the stomata. After a shower of rain, or when a 

 plant is watered, it having perhaps been suffering from drought, 

 a general freshening-up is shown. A common error is to sup- 

 pose that the plant has actually absorbed the water by means 

 of the leaves and stem, whereas it has absorbed it through the 

 roots, the humidity of the air contiguous with the leaves 

 preventing in addition any further great loss of water by 

 evaporation from the interior of the leaves. 



The passage of the water through the conducting-tubes in 

 the wood of the root, stem and branches to the leaves has to 



