Stem elongation and concomitant acceleration of
flowering are well known responses of some higher
plants to treatment with gibberellin (2, 3, 7, 8, 19, 20).
It is clear that responsive biennials, such as henbane
(Hyoscyamus niger L.) and carrot (Daucus carota
L.) must reach a certain stage of development before
either cold or gibberellin is effective in promoting seedstalk
elongation and flowering (4, 5, 9, 19). Thus,
in carrot a minimum root diameter of about 1 cm must
be attained before flowering may be induced (4, 19).
The flowering behavior of the biennials is in contrast
to that of winter annual plants such as head lettuce
(Lactuca sativa L.) and endive (Cichoritum endivia
L.). The winter annuals, one of which is discussed
in this paper, have only a quantitative requirement
for cold. Flowering is hastened by a short period
of seedling vernalization followed by a regimen of
long days and high night temperatures (6, 10, 11, 12,
13, 14, 16, 18, 19). Application of gibberellin at any
time after seed germination promotes stem growth
and subsequent flowering of endive and of lettuce.
The questions which the present experiments were designed
to answer are: a) to what extent does gibberellin
replace the cold and/or long day requirements
for flowering of endive, and b) to what extent does
gibberellin overcome temperatures unfavorable for
seedstalk elongation
