Variations and Adaptations in Animals and Plants 723 



Ecologic variations result from a fixed relation to environment. Varia- 

 tions brought about by environment might be illustrated as follows: 

 Members of the same species of an organism differ or vary when they 

 live under entirely different environmental conditions. The same species 

 of plant will appear quite differently when grown in high altitudes and 

 when grown at sea level. 



40 



18 



£l 



21 



I I 



22 24 26 28 30 



23 25 27 29 



mllllmetera In diameter 



Fig. 357. — Diagram to show variations in snails. The diameters were measured 

 of 100 land snail shells collected from an area with uniform environment. The 

 diameters varied from 22 to 30 mm. The number of individuals of each diameter 

 is represented by the upright blocks. Observe that these variations so plotted 

 form a curve. 



According to Gradations. — Continuous variations or fluctuations are 

 common variations which occur in individuals with identical heredity; 

 they grade one into another so as to make an unbroken, graded series 

 from one extreme to the other. Examples of continuous variations are 



