HOW PLANTS FEED 21 



ure 10.) If now we evaporate the water from the glass, 

 the sugar will again appear in the bottom. 



Mineral Matter in Plants. A tea-kettle in which well 

 water is often boiled usually becomes coated inside with 

 a whitish deposit. Well water contains small quantities 

 of certain mineral substances dissolved in it. When the 

 water evaporates from the tea-kettle by boiling, these 

 minerals remain in the bottom, just as in our experiment 

 the sugar remained in the basin after the water evaporated. 

 We learned in Lesson 3 that plants take up water, and 

 that this water passes off as vapor from the leaves. The 

 water thus taken up by plants comes out of the soil and 

 so has certain mineral substances dissolved in it. When 

 this water is transpired from the leaves, the minerals 

 remain, just as they remain in the tea-kettle when the 

 water evaporates from it. Some of these mineral sub- 

 stances are required by the plant for food. Aside from 

 water, the roots can take only dissolved substances. 



Other Matter in Plants. We have now learned how 

 plants secure the mineral part of their food. But are 

 plants formed entirely of mineral matter? We can 

 answer this question by a simple experiment. Mineral 

 matter will not burn. If we burn a little bunch of hay or 

 straw, the part that will not burn, the ashes, is mineral 

 matter. The ashes of the hay were brought up from the 

 soil in the water that was taken up by the grass roots. 

 When we burn a substance, we separate it to some extent 

 into the parts that once came together to make the sub- 

 stance. Nearly all of the part of the hay that passes 

 off into the air in burning came out of the air while 

 the grass was growing. 



