72 FUNDAMENTALS OF FRUIT PRODUCTION 



to the increase in fruit size that can be effected through increased 

 moisture supply is shown by many irrigation experiments. For instance, 

 with peaches on a deep gravelly loam in Utah, it was found that 31 

 acre-inches of irrigation water gave as large size and as large yields as 

 62 acre-inches under the same conditions. ^^ 



An interesting moisture relation within the plant itself that often 

 affects fruit size is pointed out by Chandler. ^^ He shows that the con- 

 centration of the sap within the leaves of the tree is higher than that 

 within its developing fruits. Consequently in times of drought, when 

 the roots are unable to supply the amounts transpired, the leaves actually 

 can withdraw moisture from the fruits, even to the point of causing 

 wilting while the leaves themselves remain turgid. This not only checks 

 temporarily all increase in fruit size but may result in a reduction. Chan- 

 dler cites several instances in which, under these extreme conditions, 

 more disastrous results occurred in cultivated than in uncultivated 

 orchards. Cultivation had been given largely for the purpose of con- 

 serving moisture; nevertheless toward the end of a long drought when 

 the moisture supply of both cultivated and uncultivated orchards was 

 approaching the wilting coefficient, the trees in the cultivated orchard 

 suffered more because they had larger leaf systems and required more 

 water to support them. Had summer pruning to reduce the leaf systems 

 been done promptly in these cases, evaporation would have been 

 reduced and wilting of the fruit prevented. Chandler states, however, 

 that summer pruning for the purpose of increasing fruit size through 

 reducing leaf area has not been successful. 



Yield. — The increases in yield from an increased moisture supply, up to 

 the optimum, are in general still more striking than the increases in size 

 because of the indirect effects of moisture through better fruit setting 

 and the formation of more fruit buds. 



A striking illustration of the influence of rainfall upon yield is recorded 

 for the palm oil tree (Elaeis guineensis) in the British Colony of Lagos. 

 Data showing the yearly rainfall and the yearly exports of palm oil and of 

 palm kernels are condensed in Table 35. The following quotation fur- 

 nishes comment on these data: 



"The yield of fruit from the palm oil tree (Elaeis guineensis) varies according 

 to rainfall. With a sufficiency of moisture the tree flowers every five or six weeks, 

 and bears eight or nine mature bunches of fruit in the year, but if the rain supply 

 is scanty the tree flowers only every ninth or tenth week, and the annual yield 

 is reduced to about five bunches. In normal times the Elaeis bears eight heads 

 (so-called nuts) in the year, but it follows a similar habit to the cocoanut, the 

 heads being formed spirally in the axils of the leaves at regular intervals, which 

 are long or short, according as the season is favorable. The mischief arising from 

 insufficient rainfall does not finish with the number of heads, for the oil is 

 extracted from the fiber of the thin outside layers of the fruit, which are either 



