PLANT CHEMISTRY 103 



To the third pot add nothing. Label each of the pots, and 

 in each set a couple of young plants or sprouted seed of corn, 

 wheat, or whatever is at hand. Water the pots, whenever 

 necessary, with the rain or snow water, lukewarm. You will 

 presently see a difference in the three plants. Describe this 

 in the note-book, and explain it. 



There is another thing which chemistry has taught us to do 

 to the soil. Plants sometimes suffer when there is too much 

 acid in the soil. If plants do not grow well in our garden 

 earth, we, can test it for acid by means of a strip of litmus 

 paper bought at the druggist's. It is blue, but when buried 

 in a tumbler of muddy acid soil, it will turn red. This test 

 should be made with care, and the paper should not be 

 handled with damp fingers, for they themselves are likely 

 to be acid. If upon testing a soil we find it acid, we can 

 improve it by adding lime. This we can do to a handful of 

 soil in the schoolroom by means of a little limewater; but 

 in the garden, lime is scattered and raked in. Thus for the 

 second time we find that lime is good for soils. But it is 

 not a plant food ; it is rather a soil improver. 



There is no need, at present, to go deeper than this into the 

 chemistry of soils. But the little that we have" learned will 

 be very valuable in our work. 



REVIEW QUESTIONS 



1. What are chemical elements ? Compounds? Name a few. 



2. What makes up the largest part of any growing plant ? 



3. What compound makes up the next largest part ? Where does 

 it come from ? 



4. What elements do we need to supply to a plant ? Why ? 



5. Can you find a good reason why cheap fertilizers are expensive ? 



6. What is the special value of nitrogen ? How can it conven- 

 iently be supplied ? 



7. How can we tell if a soil is sour ? How can we sweeten it. ? 



