WATER-STRESS BEHAVIOR OF PIMA COTTON. 



13 



It has been stated by both Lloyd (19) and Balls (3) that there is 

 always observable a steady increase in the percentage or relative rate 

 of shedding of squares and bolls as the season advances, the first 

 squares formed having the lowest relative shedding rate and the 

 highest rate occurring just before the plants begin to show a retarda- 

 tion of growth near the end of the season. Lloyd would explain this 

 as probably due to the fact that the adjustment of the plant to its 

 environment is not as good during the latter part of the fruiting 

 season as earlier. Having observed the records of well water in 

 which the water was gradually lowered during the summer and con- 

 cluding therefrom that the moisture content was reduced in ever- 







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 tfAr/L. M9r JUA/S <JULY /IOgGs? &SP71EMBER 



Fig. 2. — Moisture content of the deeper layers of soil and the mean percentage of bolls 

 shed on the basis of the total bolls produced during the same week. 



increasing depths of the soil as the season advanced, he reasons that 

 this condition places a more severe tax on the plant and causes an 

 increasing rate of shedding. Though Lloyd (18) presents no soil- 

 moisture data to substantiate his hypothesis as to the relation of this 

 factor to shedding, it appears from the results secured by the writer 

 and confirmed by four years of observation of the water relations 

 of the Egyptian cotton plant under arid conditions that Lloyd's 

 opinion is well founded. 



The amount of square shedding at Phoenix was so small at the 

 commencement of the fruiting activities that no attempt was made 

 to record the rate after the first three or four weeks. The curves 

 representing boll shedding do not show the rate of shedding increas- 

 ing with the advance of season to the marked degree exhibited in the 

 curves presented by Lloyd. This, however, is not surprising when 



