Some plants require exposure to light for a period exceeding a well-defined critical duration. These plants are known as:

The relation of flowering to the lengths of light and dark periods 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. These results indicate that flowering:

Dark periods (hours)	Flowers formed (Light: $4$ hrs / $16$ hrs)
$8$	$0$ / $0$
$10$	$0$ / $0$
$12$	$4$ / $6$
$14$	$5$ / $7$
$16$	$5$ / $8$

Photoperiodism was first characterised in

What is the effect of temperature and light on plant growth regulators in plants?

Which of the following statements are $INCORRECT$ with respect to phytochrome?
$i$. Phytochrome is a light-receiving proteinaceous pigment present in the leaves of plants.
$ii$. Phytochrome pigment exists in two forms.
$iii$. Two forms of phytochromes are interconvertible.
$iv$. Phytochromes are located in the chloroplast of green cells.
$v$. Phytochrome $P_r$ form inhibits flowering in $LDP$ during the dark period.

$Nicotiana$ $tabacum$,a short-day plant,fails to flower when exposed to a light duration longer than its critical period. Explain.