Water only One of the Necessary Plant -foods 15 



rains and sweet irrigation waters do in the soil, we 

 may not be surprised to see the large yields of grass 

 or of potatoes or corn it is capable of helping the 

 soil and the sunshine to bring forth as the product 

 of a summer's work. 



WATER ONLY ONE OF THE NECESSARY PLANT -FOODS 



In view of the facts which have just been pre- 

 sented, it is not at all strange that the ancient Egyp- 

 tian and Grecian philosophers, with their lack of exact 

 knowledge and under their arid climatic conditions, 

 should have come to believe that water is the sole 

 food of plants ; nor that this opinion should have 

 been held until nearly the beginning of the eighteenth 

 century. As a matter of fact, water does contribute 

 more than half of the materials which make up the 

 dry matter of plants, and, as water, it constitutes from 

 three -fourths to more than nine -tenths of their green 

 weight. 



But while these are the facts, and while it is true 

 that abundant and timely rains do make compara- 

 tively poor soils produce large yields, it must not be 

 inferred that, with ample and timely supplies of water 

 applied to the soil, all else may be neglected and the 

 hope entertained that any agricultural soil will thus 

 be held up to a high state of productiveness for an 

 indefinite term of years. 



It is a matter of universal experience that sewage 

 waters, not contaminated with poisonous compounds 

 and not too highly concentrated, cause lands to give 



