THE ROOT 



67 



influence the direction and rapidity of the 

 current, but does not furnish the motive 

 power, which evidently comes, in part at 

 least, from the roots, and is the expression 

 of their absorbent activity. 



EXPERIMENT 50. To SHOW THAT ROOTS 

 GIVE OFF ACIDS. Lay a piece of blue lit- 

 mus paper on a board or on a piece of glass 

 slightly tilted at one end to secure drainage. 

 Cover the surface with an inch of moist 

 sand and plant in it a number of healthy 

 seedlings. Acids have the property of 

 changing blue litmus to red ; hence, if you 

 find any red stains on the paper where the 

 roots have penetrated, what are you to 

 conclude ? 



The kind of acid given off may differ ac- 

 cording to the soil the roots are growing in 

 and the solutions it contains. Carbon 

 dioxide has a slight acid reaction and is 

 exhaled in varying quantities by all roots. 



EXPERIMENT 51. CAN THE ABSORBENT 

 POWER OF ROOTS BE INTERFERED WITH ? 

 Place the roots of a number of seedlings 



with well-developed hairs in a weak solution of saltpeter 10 grams (about 

 of an ounce) to a pint of water, and others in a stronger solution say 

 30 grams, or 1 ounce, to a pint. Try the same experiment with weak 

 and strong solutions of any conveniently obtainable liquid fertilizer. 

 After 45 minutes or an hour examine the roots under a lens and note the 

 change that has taken place. What has gone out of them ? What caused 

 the loss of the contained sap ? 



EXPERIMENT 52. To TEST THE WEIGHT OF SOILS. Thoroughly dry 

 and powder a pint each of sand and clay, measure accurately, and balance 

 against each other in a pair of scales. Which weighs more, bulk for bulk, 

 a "light" soil, or a "heavy" one? 



EXPERIMENT 53. To TEST THE CAPACITY OF SOILS FOR ABSORBING AND 

 RETAINING MOISTURE. Arrange, as shown in Fig. 82, a number of long- 

 necked bottles from which the bottom has been removed. This can be 

 done by making a small indentation with a file at the point desired and 

 leading the break round the circumference with the end of a glowing wire 

 or a red-hot poker. The crack will follow the heated object with sufficient 



FIG. 81. Arrangement for 

 estimating the force of root pres- 

 sure : s, stub of the cut stem ; g, 

 glass tubing joined by means of 

 the rubber tubing, t, to the stem ; 

 ra, mercury forced up the glass 

 tube by water, w, pumped from 

 the soil by the roots. 



