4.4 Control Of Flowering In Plants

Question 1

Photoperiodism - definition

Answer 1

Response of plants to relative periods of light and dark.

Photoperiodism involves the detection of day length and a reaction to this length of light and dark.

Question 2

Critical day length.

Answer 2

For some plants the length of the day is essential for triggering of a response such as flower initiation - this is referred to as Critical Day Length.

Question 3

Effects of photoperiod on some plants

Answer 3

Autumnal colour in deciduous trees and shrubs
Plants can be triggered to produce underground storage structures eg.bulbs.
Exhibit vegetative changes.

Question 4

Categories of day length.

Answer 4

Short day plants.
Long day plants.
Day length neutral plants.

Question 5

Short day plants.

Answer 5

Examples:
Chrysanthemum
Euphorbia pulcherimma.

Flowering is triggered when the day length is SHORTER than the critical length period.
Vegetative growth (but no flower buds) continues when day length exceeds critical length.

Outside these plants usually flower in autumn or winter.

Question 6

Long day plants.

Answer 6

Examples:
Phlox paniculata.
Campanula carpatica.

Flowering is triggered when the day length is longer than critical period.
Only vegetative growth when day length is below a critical length.

Outside these plants usually flower in the spring.

Question 7

Day length neutral plants.

Answer 7

Not sensitive to changes in the day length.
Flowering and vegetative growth patterns are not tied to photoperiod.

Eg.Lycioersicum esculentum