EFFECT OF BARRIERS ON PLANT LIFE 305 



foothold within the jar. If such a thing happens, food will be 

 manufactured within their bodies, a new food supply arises for the 

 animals within the jar, and a balance of life results. 



Practical Exercise 14. Look for examples of ecological succession in your 

 llaboratory. Any evidences of this ? Where ? 



Visit a burned-over area and note the new plants which come up. How 

 Ido they differ from the old ones? 



Might a garden show examples of ecological succession? Give examples. 



Self-Testing Exercise 



(1) are always taking place in animal and plant (2). 



iNew (3) invade areas which have been (4) 



I (5), or animals (6) or shift their (7) 



because of lack of (8) or other causes. Such a change is 



[called an (9) (10). 



PROBLEM VHI. WHAT DO WE MEAN BY GEOGRAPHIC 

 DISTRIBUTION OF LIVING THINGS? 



Range of plants and animals. Plants and animals inhabiting a 

 given territory or area are called the flora or fauna of that range or 

 area. We find out the range of a given form by collecting it in 

 as many places as possible. This kind of work is interesting to 

 boys and girls because they can determine the range of certain 

 plants and animals in their own locality. 



The areas in which given species of plants or animals are found 

 may be very limited or very wide. Some trees, for example, the 

 western redwood, have a rather limited range in the extreme north- 

 west while the western yellow pine or the eastern hemlock has a 

 much wider range. Some of these areas were much larger in 

 ancient geological times than they are now. That certain areas 

 have become discontinuous is seen in the distribution of elephants, 

 which once were found over a large part of the earth's surface. 

 Man may reduce or increase the range of an animal, as when he 

 nearly exterminated the buffalo, or introduced a pest such as the 

 orange scale in California or the gypsy moth in Massachusetts 

 or the chestnut canker on Long Island. 



Barriers and their effect on plant and animal life. Any one who 

 has seen the Sierra Nevada mountains and knows the difference 



