CHAPTER X 



ROOTS 



Plants, as we have seen, need a constant supply of 

 water for transpiration and for growth. They cannot, as 

 a general rule, take this in by their leaves, and therefore 

 must take it in by their roots; and without water the roots 

 cannot take up and supply to stem, branches, leaves, 

 flowers, and fruit that mineral matter without which the 

 plant cannot exist. 



Before examining the way in which the roots perform 

 their work of supplying all parts of the plant with liquid 

 food, we must briefly consider where the water comes 

 from. 



For if, as has been said, the ordinary rainfall in Eng- 

 land for the whole month of July is about three hundred 

 tons, and if an acre of pasture-grass transpires more than 

 three thousand tons in the same time, it is quite evident 

 that the demand far exceeds the supply from the clouds. 

 Moreover, the grass does not get even the full benefit of 

 that which does fall, for a very large proportion is either 

 at once evaporated from the soil, or is drained away into 

 ponds, lakes, streams, or rivers. Of the ram which falls 

 .in England between April 1st and October ist, it has been 

 calculated that ninety per cent is evaporated from the soil 

 and returned to the air. From the air, however, the soil 

 again absorbs it; for though leaves do not absorb moisture 

 from the air, the soil does. 



lOO 



