My Campbell's Biology textbook discusses photoperiodism of plants and introduces us to short-day and long-day plants. What I don't understand is why short day plants will not flower if they are exposed to a very brief flash of light during the night, even if that brief period + the actual day's length is still less than their critical day length? Or, put more concisely:
Length of Flash + Length of Day < Critical Period <-- Why does the short-day plant not flower?
The following diagram is from Campbell's and makes no sense to me, because it also seems like a long-day plant which is exposed to a brief period of light during the dark will flower even if that period of brief light + its actual day's length is not greater than its critical period (i.e. it never fulfilled the pre-requisite for flowering).