THE FARM, AND OUR FOOD SUPPLIES 157 



Arrange the chimneys so they are supported upright with 

 their lower cloth-covered ends in a pan containing about an 

 inch of water. 1 From time to time observe the upward rise 

 of the water into the chimneys by capillary action, both its 

 elevation and its rapidity of ascent. Account for any dif- 

 ferences noted. 



As the water in the surface layers of soil in the field becomes 

 exhausted by plant growth, or by evaporation, whence may 

 it be replenished without rainfall, and how? 



7. Counterbalance two baking powder cans that have 

 been filled somewhat more than half full of moist soil made 

 compact by jarring, the top of the soil in one of the cans hav- 

 ing a half-inch layer of fine dry loam (or some dust). Ob- 

 serve the scales from time to time through a day or two as 

 they are left undisturbed. Interpret the significance of any 

 loss of equilibrium. What relation has this to the cultiva- 

 tion of crops during the growing season? 



8. Watch closely for the escape of any bubbles of air from 

 a test tube one half full of soil as an inch or more of water is 

 poured in upon the soil, and account for the bubbles. What 

 is a possible cause of the dying of plants in pots where any 

 excess of water poured in cannot drain off. Account for a 

 possible crop failure on low grounds in wet seasons. 



USEFULNESS OF PLANTS TO MAN 



1. From your own personal experiences, and from any 

 other sources of information, prepare lists of four items each 



1 Through the upper side of a box from which the front has been removed 

 bore holes of a size such as to allow the small ends of the chimneys to pass 

 and to hang suspended in full view. 



