THE SOIL AS RELATED TO PLANTS. 97 



ma)- become so strongl)- acid in its character as 

 to be unfavorable or unproductive to certain 

 valuable species of plants. This condition may 

 exist not only on swampy or peaty soils, but 

 also upon well-drained soils. Soil may be easily 

 tested for acid by thoroughly moistening it and 

 placing in it a strip of blue litmus paper. If the 

 color of the litmus paper is changed to red the 

 acid of the soil is too strong for plant growth, 

 and the addition of lime will prove beneficial. 



Another way in which the need of lime in a 

 soil in shown is by the plants which it will nat- 

 urally produce. Plants known to be character- 

 istic of acid soils are : bird's-foot violet ( Viola 

 pedatd), wild or beard grass (^Ajidropogon scopa- 

 rius), wood-rush {^Liizzila campestris), and, as 

 soon as the soil is cultivated, the common sorrel 

 [Riunex acetosella), while those plants which are 

 unable to make any satisfactory growth upon 

 such soils are the red clover, lettuce, beets, tim- 

 othy, and spinach.* 



Exercise 4. — {a) Collect small samples of soil from 

 various places where the vegetation might lead one to 

 suspect the presence of acid soil. 



{b) These samples of soil should be taken from about 

 two to four inches below the surface, and each sample 

 carefully labeled as to exact location from which it was 

 obtained. 



(r) These samples should be taken to the laboratory, 



* Roberts' Fertility of the Soil, p. 318. 



