193 



IRRIGATION AND ROOT MANAGEMENT. 



How PLANTS ABSORB WATER. 



Plants, flowers, and fruits are made up mostly of water. 

 Analysis shows that there is as much as 901bs. to 941bs. of water in 

 every lOOlbs. of some of the more succulent fruits and vegetables, 

 such as asparagus, cabbages, cucumbers, lettuce, melons, rhubarb, 

 tomatoes, and strawberries ; as much as 801bs. to 851bs. of water in 

 every lOOlbs. of such fruit as apples, apricots, grapes, lemons, and 

 pears ; green fodders contain 60 to 85 per cent, of water according 

 to their state of maturity. It is essential that the contents of the 

 cells which enter into the structure of the growing plant should be in 

 a half -liquid condition in order that nourishment and construction 

 material should be carried and distributed wherever required, be it in 

 the stem, the tender buds, or the ripening fruit. When the cells cease 

 to be distended with fluid sap they get flaccid and the plant wilts. 

 Unless this state is promptly remedied by an influx of sap these 

 cells thicken, they lose their elasticity, the plant first gets stunted 

 and finally dries up and dies. The water necessary for plant 

 growth is absorbed by the hair-like rootlets issuing from the 

 stronger roots which penetrate the ground in search of food and 

 moisture ; it does not, however, enter into the circulation of plants 

 quite pure, but contains in solution variable quantities of substances 

 which plants feed upon. From these rootlets it is passed on from 

 cell to cell, by a process of diffusion, first along the larger roots 

 which anchor the plant to the ground, thence to the stem, on to the 

 branches, the buds, leaves, and fruit. 



That cell-to-cell motion, or that diffusion of the nourishing sap, 

 from the capillary rootlets to the tip of the branches, is quickened 

 by evaporation. 



The evaporating organs of the plants are the leaves. These, 

 when fanned by the breeze, allow a considerable amount of 

 moisture to escape through the stomata or breathing pores. In 

 bright daylight these pores open to allow the admission of carbon 

 and of oxygen to the working cells of the leaves. As this takes 

 place a good deal of the moisture which saturates the air in the 

 intercellular spaces of the leaves escapes to the drier outside air. 

 A vacuum is thus created, and more moisture exudes from the 

 gorged cells to replace the amount lost through evaporation. In 

 this manner a current of sap is created from the rootlets upwards 

 towards the branches. 



Under certain circumstances this current may run quicker than 

 the plant is able to absorb moisture from the ground. This is 

 noticeable on a dry, hot day, when the plant flags. 



This being so, it is easy to understand that other conditions 

 of soil texture and of particular plant requirements being alike, a 

 given field crop, or trees of the same sorts and age, will show signs 

 of wilting and need for water much sooner in the drier air of the 



