The Plant and Its Environment 



II 



Development of plants influenced by the environment. Each 

 factor of the environment affects the growth of every plant. We 



Fig. 4. Results of an experiment to show effects of environmental factors (light and mois- 

 ture) on the growth of potato shoots: A, light but no water; B, light and water; C, water 

 but no light. 



are all familiar with the fact that light may determine the position 

 of leaves and stems ; that drought may reduce the size of a plant ; 

 that gravity has something to do with the upward growth of 

 stems and the downward growth of roots ; and that insect in- 

 juries and plant diseases may reduce the vitality of plants so that 

 they produce neither flowers nor fruits. So the texture and the 

 fertihty of the soil, the temperature of the soil and air, and all 

 the other environmental factors influence the plant's develop- 

 ment and its growth. Successful farmers know that they can- 

 not secure vigorous plants and profitable crops except under 

 favorable conditions of hght, temperature, moisture, and soil. 



Limiting factors of plant growth. Wherever plants grow the 

 several environmental factors are not all equally favorable. 

 One or more conditions may be somewhat unfavorable, and when 

 this is the case these unfavorable factors interfere with certain 

 physiological processes, and the final form of the plants is greatly 

 modified. Just as the strength of a chain is determined by the 



