Wright Pierce 

 In a desert, we find that plants are succulent and have spines, bristles, and rigid walls. Why? 



by two general sets of. factors in their environment, forces and 

 things. These forces are temperature, light, gravity, and, to a 

 lesser extent, such factors as the presence or absence of winds, the 

 presence or absence of electrical storms, and the pressure of the 

 i atmosphere. 



The things that affect living plants and animals are natural or 

 ; man-made objects with which they come in contact, such as 

 foods of all kinds and the presence of other living or dead plants 

 and animals in the vicinity. 



Temperature. We have already observed the effect of tempera- 

 ture on the growth of seedlings. We know that certain tropical 

 forms of life flourish only in heated areas, and that there are plants, 

 such as the lichens of the frozen tundras of the north, that will 

 grow only in extreme cold. Animal life can equally well be shown 

 to be dependent upon temperature conditions. One of the most 

 striking examples of this was seen in 1882 when fish, abundant in 

 the Gulf Stream, were found dead and dying by the millions in a 

 large area off the eastern coast of the United States. This 

 i catastrophe was believed to have been caused by the cold arctic 

 (current being shifted by long-continued easterly and northerly 

 winds, the cold water displacing that of the Gulf Stream, thus 



