FUNCTIONS OF THE ROOT 23 



up by the roots in the form of very dilute solutions 

 of chemical salts, such as calcium nitrate, potassium 

 phosphate, magnesium sulphate, sodium chloride. 



The solution of these salts must be very dilute, for 

 experiments have shown that if plants are grown in 

 water there must not be more than one part of any of 

 these salts in five thousand of water. It is on this 

 account that such large quantities of water have to be 

 taken up from the soil and passed out again through 

 the leaves into the air. By experiments and careful 

 measurement, it has been found that in India a crop 

 plant such as Cholam requires an immense amount 

 of water, several hundred and even a thousand times 

 its weight to bring it to maturity. As only a very small 

 proportion, less than twenty per cent of its weight, is 

 due to mineral matter, and as a plant cannot get rid of 

 mineral matter that has once been absorbed, the con- 

 centration of these salts dissolved in the water taken 

 from the ground must be very low, probably consider- 

 ably below one part in 10,000. 



7. The functions of the root then are three. 

 First, to fix the plant firmly so that it cannot be 

 blown over by an ordinary wind, or pulled up completely 

 by a grazing animal. Second, to absorb and pass 

 upward from the soil the large quantities of water 

 evaporated daily from the leaves. Third, to take upv 

 the necessary mineral substances and solutions and 

 pass them on to the shoot. 



8. The living substance of a plant requires air, that 

 is to say, oxygen, just as animals do. We breathe 

 in air ; the oxygen of it passes into the blood and is 

 circulated to all parts of the body, where it combines 



