1. Photoperiodisms Photo = light Period = time

2. Photoperiodism A physical response to photosynthesis, the length of day verses the length of night Plants that flower under certain day length conditions are said to be photoperiodic.

3. Critical Length The length of daylight hours a plant requires in order to produce flowers Could be determined by: Time (1 day or weeks) Temperature Location

4. Photorecptors Specialized plant cells that monitor the amount of light (like having eyes) Plants are actually more sensitive to the length of darkness than of light.

5. Short-day plants Plants that require a light period shorter than the critical length Plant will bloom only in time less than the critical length flowers in early spring or late fall Ex: poinsettias, strawberries, primroses

6. Long-day plants Plants that require a light period longer than the critical length Plant will bloom only in time more than the critical length flowers in the summer Ex: spinach, lettuce, hembane

7. Day-neutral plants Not affected by the amount of daylight Blooms in spring, summer, and fall Ex: cucumbers, sunflowers, rice

8. Photoperiodism Short-dayLong-dayDay-neutral Light Length Less than critical length More than critical length Not affected BloomsSpring, FallSummer Spring, Summer, Fall Examples Poinsettias, Strawberries, Primroses Spinach, Lettuce, Hembane Cucumbers, Lettuce, Rice