WATER-STRESS BEHAVIOR OF PIMA COTTON. 



7 



did not receive their first irrigation until June 26. (PL I.) Through- 

 out July and August the plants in plats 1 and 2 continued to grow 

 more rapidly and exhibited a more luxuriant growth. This is shown 

 in the diagrams in figure 1, which gives the growth in inches per 

 plant per week and the average percentage of available moisture 

 per week in the upper 4 feet of soil in each plat. 



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Fig. 1. — Average percentage of available moisture per week in the upper 4 feet of soil 

 in four plats and the average increase in growth of the main stem of the plants per 

 week. 



During periods in the summer when very high temperatures were 

 prevailing and when transpiration by the plant was at its highest, it 

 was observed that the plants on plat 1 exhibited what might be 

 termed a " water stress " in more pronounced degree than those on 

 any of the other plats. This stress was made manifest by the wilted 

 appearance of plants on plat 1, which occurred more frequently and 



