Types of plants depending upon photoperiodism :
1. Short day plants : These plants produce flowers in winter. They are also called long night plants e.g. Chrysanthemum, tabacco etc.
2. Long day plants : These plants produce flowers in summer, when the days are long and duration of light is above critical point e.g. Melon, Momordica, Water-melon, Lady's finger plant etc.
3. Short long day plants : These plants need short photoperiod for initiation and long photoperiod for blossoming of flowers e.g. Rye, Campanula etc.
4. Long short day plants : These plants need long photoperiod for initiation and short photoperiod for opening of floral buds. They give flowers between summer and winter e.g. Cestrum, Bryophyllum etc.
5. Intermediate plants : These plants need definite photoperiod for flowering e.g. wild kidney bean.
6. Day neutral plants : These plants produce flowers in both winter and summer seasons. They do not need any specific photoperiod e.g. Sunflower Tomato etc.
Auxin was isolated by F.W. Went from tips of coleoptiles of oat seedling.
Auxins are of two types :
(1) Natural auxins : These are naturally occuring auxins, isolated from plants and are regarded as phytohormones e.g. IAA. NAA etc.
(2) Synthetic auxins : These are synthesized by artificially e.g. IBA 2,4-D etc.