14 BULLETIN 521, U. S. DEPAETMENT OF AGRICULTURE. 



rise of capillary water depend ? Of what practical importance is the 

 relation of capillary water in soils to the farmer? How will it affect 

 his management of soils of different types ? 



Note. — As a preliminary to this exercise Capillarity may be demonstrated to 

 the class by dipping a cube of sugar in water colored with ink. 



Exercise 11. — Use of Water hy Plants. 



Purpose: To show how plants give off moisture and to give an 

 idea of the amount of water used by plants. 



Directions : Start a pea vine or some other plant which will grow 

 Aigorously in a flower pot. After the plant is growing well cover 

 the top of the pot with a piece of cardboard somewhat larger than 

 the top of the pot, cutting a slit in the board for the plant. Seal the 

 slit with pitch, wax, or tallow so that no moisture can evaporate from 

 the soil. Cover the plant with a glass jar and set in a warm, sunny 

 place. If the jar is cooled by wrapping it for a minute or two in 

 a cloth wrung out of cold water, moisture will condense on the inner 

 surface of the glass. 



To determine the quantity of water used, the same plant may be 

 used if there is a space to hold water between the surface of the soil 

 and the cardboard. Water should be applied as needed, lifting the 

 cardboard to apply it. Weigh all water given, keeping up the test 

 for a month or as much longer as convenient. At the end of the test 

 dry the plant thoroughly, weigh it, and then determine the relation 

 between the dry matter and the water needed to produce it. 



Record and report: Each student should make a record of the 

 water used and make a written report of results in which he should 

 answer the following questions: Where does the water on the glass 

 come from ? How is this water given off by plants ? Is all water ab- 

 sorbed by the roots given off by the leaves ? What is the function of 

 water in the plant ? About how much Avater is used to make a pound 

 of dry matter in the plant tested ? How does this test agree with pub- 

 lished reports? 

 Exercise 12. — Effect of Mulching on Conservation of Moisture. 



Purpose: To test the efficiency of different mulches. 



Directions: Six cans or pots of equal size should be filled with 

 equal quantities of loam soil of uniform grade. Fill within 2 inches 

 of the top and wet thoroughly with equal quantities of water. These 

 cans should then be treated with mulching material as follows: (1) 

 Left as a check, (2) cover with IJ inches of soil and pack it down, 

 (3) cover with the same amount of the same kind of soil, but keep 

 it loose by stirring from time to time, (4) cover with 1^ inches of 

 gravel, (5) cover with 1^ inches of fine road dust, and (6) cover with 

 1| inches of chaff, sawdust, or bits of dry leaves. Keep all cans under 

 similar conditions. Weigh morning and evening for five days. 



