1 8 AGRICULTURE. 



How MINERAL FOOD GETS INTO THE PLANT. We have 

 before learned that water goes into the plant through the 

 roots and passes out by the leaves ; there must therefore 

 be a movement of the water through the plant ; and we 

 thus conclude that the water can carry along with it into 

 the plant, and through it, some substances taken up in solu- 

 tion from the soil, that is, that it will take into the plant 

 whatever it finds in the soil that can be dissolved. This is not 

 quite the case, for the roots appear to have the power, in large 

 measure, of taking up the substances that the plant requires ; 

 the roots have a certain amount of what may be called 

 " selective " power. 



One thing more may be mentioned in connection with the 

 taking in of food by the roots; there is a small amount of 

 weak acid found in the ends of the roots, so that wherever 

 the fine, hairy rootlets come into contact with the soil they 

 are helped by this weak acid to dissolve small quantities of 

 material that the water alone, without this acid, could not take 

 up. It is because of this that we frequently find the marks of 

 plant roots on the face of hard rocks, showing where the roots 

 by their acids have eaten out some of the rock. 



When we burn wood in the stove we have left what is called 

 the ashes. If we burn up some straw, or grain, in fact any 

 kind of a plant, we have left some ashes. This ash is earthy 

 in nature. Sometimes it is called the " mineral matter " of the 

 plant. It has all gone into the plant by way of the roots, dis- 

 solved in the water of the soil. When this ash or mineral 

 matter is taken apart and examined by a chemist, it is found 

 to contain such substances as compounds of lime, soda, and 

 potash. From 100 pounds of plants taken, we get one to five 

 pounds of ash or mineral matter; we therefore say, that the ash 

 or mineral matter forms from one to five per cent, of the whole 

 plant, and it has all come from the soil. 



The mineral matter of the soil, after being dissolved in the 



