II. THE SURROUNDINGS OR ENVIRONMENT OF LIVING 



THINGS 



Environment. A plant or an animal living on the earth may be 

 said to come in contact with air, water, and soil. It may be influ- 

 enced by light, varying conditions of temperature, of the atmosphere 

 or water, the presence or absence of food materials, and some other 

 things. We shall later see that the sum total of these various fac- 

 tors, acting upon the living thing, may cause great changes to take 

 place in the structure or habits of a plant or animal. The surround- 

 ing forces which act upon living things form their environment. 



In order better to understand what a living plant or animal 

 takes from its environment, we must find out something about the 

 air, water, and the soil, for it is with these factors that the plant 

 and the animal are in immediate contact. 



Problem I. A study of the common elements in the en- 

 vironment of living things. (Laboratory Manual, Prob. 7.) 1 

 (a) Nitrogen. 



(ZO Oxygen and oxidation. 

 Cc) Hydrogen. 

 (d) Carbon and Carbon dioxide. 



The Composition of the Air. If we 

 invert a large bell jar over a deep 

 tray containing water, having pre- 

 viously placed a float holding a bit of 

 burning phosphorus upon the surface 

 of the water, we find that as the phos- 

 phorus burns, the water slowly rises in 

 the jar. After a little the phosphorus 

 goes out. The water now displaces a 

 volume equal to about one fifth of the 



Experiment to show the amount 

 of nitrogen present in the air. 



1 Sharpe, A Laboratory Manual jor the Solution of Problems in Biology, American 

 Book Company. 



HUNT. ES. BIO. 2 17 



