EFFECT OF COLOR, WATER AND TEXTURE 59 



Questions. (a) What is the result when a heavy soil is plowed too wet? 

 (6) Why is clay called plastic? 



(c) Why does not the sand ball harden like the clay? 



(d) What has happened to make the clay ball become so hard on drying 

 (Look up "puddled soil" in index.) 



To Study the Effect of Freezing and Thawing on a Puddled Soil. Pro- 

 cedure. Thoroughly moisten the hard clay ball obtained in the previous 

 exercise, and freeze it if the weather is cold, or use a freezing mixture. Place 

 the frozen ball in the sun to thaw out and dry. Note results. 



Questions. Explain why it is good to plow a hard, lumpy soil in the fall. 



To Determine the Effect of Salt When it is in Contact with Planted Seeds. 

 Procedure. Fill a one-gallon crock with moist loam and plant 4 kernels each 

 of corn and oats. On the first pair of seeds (corn and oat) do not put any salt; 

 on the second one pinch; on the third two pinches; and on the fourth three 

 pinches of salt. Cover with soil and observe results. Water when necessary. 



Questions. (a) In what ways does salt affect a germinating seed? 



(6) Of what importance is this fact to farmers? (See text.) 



To Note the Effect on a Plant of Growing it in Darkness. Procedure. 

 Plant corn and beans in each of two one-gallon crocks. Water both, and keep 

 at the same temperature. Keep one in the greenhouse and the other in a dark 

 room. Allow the plants to grow for 2 to 3 weeks and then test the leaves for 

 starch with tincture of iodine. (A blue color indicates the presence of starch.) 



Questions. (a) What did the plants in darkness live on? . 



(&) Why is there no starch in the leaves of the plants grown in darkness? 



(c) Why are the plants grown in the darkness white? 



(d) What is necessary in the manufacture of starch by the plant? 



(e) Why is it difficult to obtain a test for starch in the green leaves early 

 in the morning? 



To Note the Effect of Color, Water and Soil Texture on the Temperature 

 of Soils. This exercise may be set up and students observe results. 



Procedure. Fill 12 one-gallon crocks within one-half inch of the top as 

 indicated below. Pack the soils uniformly and carefully, and have crocks 

 filled to the same mark. This is to be done one day. Set the prepared crocks 

 where the sun will not strike them and where all will remain at the same 

 temperature till the next day. Avoid steam pipes. 



No. 1. Fill with water. 



No. 2. Dry fine sand. 



No. 3. Moist fine sand. 



No. 4. Dry fine sand with y inch of ground muck on surface. 



No. 5. Dry fine sand with Y inch of powdered slaked lime on surface. 



No. 6. Dry silt loam. 



No. 7. Moist silt loam. 



No. 8. Wet silt loam. 



No. 9. Black sandy loam (dry). 



No. 10. Light colored sandy loam (dry). 



No. 11. Moist fine sand with surface at right angles to sun. 



No. 12. Moist fine sand with surface slanting away from sun. 



Put thermometers which were previously tested for uniformity in the 

 crocks so that the bulbs are 1 Yi to 2 inches below the surface. Do not have the 

 soil cover them above the 20 mark. Put all the thermometers in at the same 

 time and read them as soon as they have had time to register. Record results. 

 Place the crocks in the sun with one side on a strip of board to incline the sur- 

 faces somewhat toward the sun. (Remember that 11 and 12 have special treat- 

 ment.) Read the thermometers every 20 minutes for 2 hours. Record results 

 in tabular form as follows: 



