ENVIRONMENT OF PLANTS AND ANIMALS 



may have come from the deeps of the sea or the far-away tropics. 

 Our environment, in a certain sense, includes anything that may 

 affect us in that place where we happen to be; this, of course, 

 includes all other living things, plant or animal, that may come in 

 contact with us during our lives in a given locality. 



All animals, and all plants as well, are surrounded by and use 

 the factors of their environment. In order to live, the potted plant 

 in the window, the goldfish in the aquarium, your pet dog at 

 home, all need air, water, light, a certain amount of heat, and food. 

 The Physicist's and Chemist's View of the Environment. — 

 Most of us have had some introduction to science and know that 



water, air, soil and rocks, the 

 bodies of living things, in short, 

 anything that occupies space, is 

 called by the physicist matter. 

 The chemist in his turn resolves 

 all matter into ninety-odd sim- 

 ple substances called chemical 

 elements. We know that air 

 surrounds us, that it has a pres- 

 sure of 15 pounds to the square 

 inch at sea level, and that, as 

 we go up from the earth's sur- 

 face, there is less and less air, 

 until it ultimately disappears at 

 a height of about 200 miles from 

 the earth's surface. We know also that the air is composed 

 chiefly of two elements, oxygen (ok'si-jen) and nitrogen (ni'tr6-jen), 

 there being about one part of oxygen to four of nitrogen. Air 

 is a mixture of these gases, together with water vapor, carbon 

 dioxide (a chemical compound), and other gases in very small 

 proportions. 



Again, by means of the apparatus shown on page 9, the chem- 

 ist and physicist, working together, have proved that water is a 

 combination of the chemical elements oxygen and hydrogen (hi'dr6- 

 jen). In this case, however, the elements are bound together so 

 closely that they form a substance called water. This substance, 

 which is always composed of a definite proportion of two parts of 



Experiment to show the amount of oxy- 

 gen in the air. A before, and B after the 

 phosphorus p is lighted. The white fumes 

 formed by the combination of oxygen 

 with the burning phosphorus settle and 

 are dissolved in the water. How high 

 does the water rise in the jar? Why? 



