Fill in the blanks:
$(1)$ ........ initiate rooting.
$(2)$ The pigment involved in photo-perception in flowering plants is ........

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)
$8$	$0$ / $0$
$10$	$0$ / $0$
$12$	$4$ / $6$
$14$	$5$ / $7$
$16$	$5$ / $8$

Define the following terms:
$(1)$ Development
$(2)$ Light period

Write a short note on Photoperiodism.

Analogy type questions:
$(1)$ Coconut milk : Zeatin : : $ABA$ : ...............
$(2)$ Phenolic acid : Seed dormancy : : Cold treatment : ...............

$A$ group of plants shows flowering in a $12$ hour day and $12$ hour night cycle. When the night phase of another group of the same plants is interrupted by a brief flash of light, flowering does not occur. In which of the following groups would you place these plants?