Ill The Great World's Farm 



are now strewn upon the bladder, they will in a short time 

 begin to pass through it into the tube, being dissolved by 

 the weak acid in its pores. 



The acid in the roots acts, it is supposed, in a similar 

 way, and thus the dissolved minerals are sucked in. But 

 as before said, living things have more power than dead 

 ones; so it may well be that roots, like lichens, dissolve 

 more than the weak acid alone would do. 



The roots take up what they themselves dissolve from 

 the particles of soil immediately surrounding and closely 

 touching them, and also what the water in the soil has 

 dissolved for them, with the help of carbon dioxide and 

 other gases. 



The water thus taken up — for what is dissolved by the 

 roots and what is dissolved by water and gas are taken up 

 together — the water thus taken up is a very weak solution 

 of various salts — phosphates and others — so weak that 

 it may fairly be compared with ordinary drinking-water. 



No water in nature is or can be perfectly pure, as has 

 been said, because it is constantly dissolving something 

 wherever it goes. And though even with what the roots 

 have dissolved the solution is still so weak as to pass for 

 ordinary water, yet it must be borne in mind that the roots 

 are constantly sucking it in, and that the leaves are as 

 constantly returning the water to the air — only the water, 

 however. The salts remain behind and accumulate day 

 by day. 



The same sort of thing on a vast scale goes on with 

 the rivers and the ocean. River water is generally taste- 

 less, though it, too, contains various salts dissolved in it. 

 This small proportion of salts is, however, being con- 

 stantly poured into the ocean, while the sun is constantly 



