126 



AMPHIBIANS 



tall or dwarf. The proportions were regular and the re- 

 currence of tall or dwarf peas was so uniform that from 

 these- and other experiments later scientists evolved defi- 

 nite laws of heredity, known as the Mendelian Laws. 



A detailed statement of these laws is beyond the prov- 

 ince of an elementary book, but it is now well established 

 that certain traits of parent plants and animals are repro- 

 duced in their offspring in regular and definite amounts 

 and proportions. 



124. Environment. — This word is used in two ways. 

 First, it refers to general surroundings such as tem- 

 perature, moisture, and 

 seasons, as they vary 

 from year to year ; and 

 secondly, to immediate 

 surroundings. The frog 

 responds to the first by 

 hibernating in the win- 

 ter ; while the second 

 phase of environment 

 may be illustrated as 

 follows : the tadpole can 

 live only in water, and 

 if the pond dries up 

 before the frog stage is 

 reached, the environment 

 has been unsuited to the 

 tadpole. This often 

 happens when the eggs 

 are laid in a temporary 

 roadside pond which evaporates long before the tadpole 

 becomes a frog. All such tadpoles die unless they are 

 able to swim to some other body of water. 



The birds that are able to fly avoid hibernating in the 



Figure 124. — Tree Frog. 

 Notice the sticky disks at end of toes. 



