Rhythmic growth and development in red oak seedlings (Quercus rubra L) grown in controlled conditions.

Under controlled culture conditions, red oak (Quercus rubra L) seedlings exhibited a rhythmic shoot elongation. The period was about 30 days: 15 days of shoot elongation plus 15 days of resting. The number of flushes varied from two to four under continuous light and from one to two with a 14 h photoperiod. After this growth stage, the shoot elongation ceased for a time, varying from 3 to 11 months depending on the individuals. During the first 20 days of this resting period, new leaves continued to be initiated. The stop in the shoot elongation was not a direct consequence of a rest in the meristem. Leave excision did not induce a renewal of shoot elongation, whereas gibberellic acid (GA(3)) did.