WATER-STRESS BEHAVIOR OE 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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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 
