90 



FIRST TEAR SCIENCE 



the ground. If necessary, push a wire down through the neck 

 of the funnel so as to free all hard-packed particles of soil in it. 



Connect the delivery tube with a bottle full of water standing 

 inverted on the shelf of a pneumatic trough. Pour water into the 

 funnel until it is full, and keep it full during the rest of the experi- 

 ment. Allow the apparatus thus arranged to stand for some hours. 

 Air will collect in the bottle over the pneumatic trough. Where did 

 it come from ? When the soil in the bottle has become entirely satu- 

 rated with water, roughly compare the amount of air collected with 

 the volume of the bottle containing the soil. What part of the soil's 

 volume is the air ? 



The smaller the soil particles are, the more surface they 

 present to water, the more they are dissolved, the more 

 food the plant hairs can reach, and the more fertile is the 

 soil, other things being equal. We have also seen by ex- 

 periment that soil contains air as well as water. Air is 

 needed if plants are to flourish, and it is necessary that it 

 be changed frequently, just as it is necessary to change 



the air in a room if 

 people are to flourish. 

 The soil must be ven- 

 tilated. Plant roots 

 must have air to breathe. 

 44. Fertile Soils. 

 Rock disintegration 

 does not furnish all the 

 complex materials 

 needed for the growth 

 of agricultural plants. 

 Only the lower orders of 

 plants, such as lichens, 

 can grow on soil as at 



MOLEHILLS. 



Showing how animals dig up the soil and 

 make it porous. 



first formed. A fertile soil is the product o ages 'of 

 plant and animal life, labor and decay. 



Plants send their filaments and roots among the rock 



