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 m 
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 Pie Ri, — Annanceaent tee 
quantities by all roots. Probably other estimating the force of root pres- 
substances, and these not a few, are actu- sure: s, stub of the cut stem; g, 
ll ted glass tubing joined by means of 
ally excreted. the rubber tubing, ¢, to the stem ; 
ExpErIMeNT 51. CAN THE ABsoRBENT 7 ™ercury forced up the glass 
tube by water, w, pumped from 
POWER OF ROOTS BE INTERFERED WITH? — the soil by the roots. 
Place the roots of a number of seedlings 
with well-developed hairs in a weak solution of saltpeter —- 10 grams (about 
4 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 sorts. — 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, ora “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 ared-hot poker. The crack will follow the heated object with sufficient 
