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 



CAUSE THE OCCURRENCE OF ACIDS. — Lay 



a piece of blue litmus 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 ? 



Carbon dioxide has a slight acid reac- 

 tion and is caused to form in varying 

 quantities by all roots. Probably other 

 substances, and these not a few, are actu- 

 ally excreted. 



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 

 I 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 tbst 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? (77.) 



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 tuijing, t, to the stem ; 

 m, mercury forced up the glass 

 tube by water, w, pumped from 

 the soil by the roots. 



