Orange varieties produce flowers during short days in
spring and autumn but also during long days in summer. It
might be assumed therefore that flower formation is not
qualitatively affected by day length and a few experiments
on the effects of day length on flower formation of 5 year
old Parson Brown and Valencia late orange trees (FURR,
COOPER and REECE, 1947) and of Washington Navel
orange cuttings (LENZ, 1964) have tended to support this
assumption. However, at least in the Washington Navel
orange, considerably more flowers are formed in the spring
flush indicating quantitative effects of short days.