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.
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.
Auxin was isolated by F.W. Went from tips of coleoptiles of oat seedling.