276 FIRESIDE SCIENCE. 



be made available in a season, as it requires nearly 

 five hundred pounds of water to bring one pound 

 of it into solution. Half a ton is a sufficient dress- 

 ing for an acre of ground. 



The element hydrogen is freely supplied to plants 

 by dew, mist, and rain, and therefore is costless 

 to the husbandman. It is only through water that 

 hydrogen can be presented to the plant, but this is 

 by no means its only important office. It enters 

 the plant as water, and it is through its agency 

 that all the various forms of food are rendered 

 assimilable. It is the liquid medium which holds 

 all the inorganic substances, and from the aqueous 

 current which unceasingly flows through the little 

 cells of plants, they are absorbed and appropriated 

 as food. 



Enormous quantities of water annually descend 

 upon the land. If the rain-fall be but twenty inches 

 per annum, it corresponds to something like two 

 thousand and twenty tons of water falling upon 

 each acre every year. Much of this is carried off 

 by evaporation, or through drainage. Still, a large 

 proportion is retained by growing plants, or passes 

 through them, aiding in most important functions. 

 It can be shown that a gallon of water passes 

 through a single plant of wheat in a season, and 

 the aqueous exhalations from the broad disc of a 

 common sunflower each day amount to six or 

 eight ounces. 



