THE WORK OF ROOTS 85 



Now empty the bottle, rinse thoroughly, and fill again 

 nearly full of water. Put into it a slip of htmus paper 

 which you have made blue as you did the one above. 



Wash the dirt from the roots of a seedling plant and 

 lower them into the bottle of water. Fasten some paper 

 about the bottle to exclude the light from the roots. 

 About forty-eight hours later, examine the litmus paper 

 to see if its color has changed. 



Conclusion. — Would you say that the roots must have 

 given off some acid into the water? How does the litmus 

 paper show this? Acids dissolve many minerals. What 

 is the use of this acid given off by the roots ? Since roots 

 of different plants feed at different depths, why is the 

 rotation of crops beneficial ? 



Write out how acids and how alkalies change the color 

 of litmus paper. 



61. How Roots hold Plants Erect. — One of the im- 

 portant functions of the roots of a plant is to anchor it in 

 the place where it is to develop, that its leaves and stems 

 may be held upright in the air. Some plants have a much 

 firmer grip on the soil than do others, and may for this 

 reason be called soil binders. Large areas of sandy soil 

 along Lake Michigan were in former years almost devoid 

 of vegetation. The shifting of the sands by the high 

 winds destroyed nearly all young plants before they could 

 become established. By the use of beach grass and 

 other grasses, the shifting of parts of this soil has been 

 stopped ; and the land that was formerly waste, is now of 

 use. The western wheat grass is much used by railroad 

 companies to bind embankments. Large tracts of land 

 on mountain sides have in the past been stripped of their 

 trees. The roots soon decayed, and great scars, gullies 

 and canons were washed out, making the land worthless 



