question_answer

The relation of flowering to the lengths of light and dark period was investigated by two experiments. In one experiment, the plants were subjected to dark periods of various lengths while the light periods were kept at 4 hours. In the second experiment, plants were kept in dark periods of various lengths while the light periods were kept at 16 hours. The number of flowers formed in relation to these periods is shown in the table

Dark periods hours	flowers formed in experimental light periods
	4 hours	16 hours
8	0	0
10	0	0
12	4	6
14	5	7
16	5	8

  These results indicate that flowering

A) Requires long days

B) Is initiated by a long light period

C) Is due to short light periods

D) Requires a minimum dark period