(a) Vernalization – In some plants, flowering depends upon  minimum temperature. The induction of flowering by exposure to prolonged cold of winter or by and artificial treatment of seeds by low temperature is called as vernalization. Presence of Oxygen is essential for it. According to some scientists, Vernalin compound is formed during vernalization that converts into Florigen or gibberllin. It is responsible for beginning of flowering.

(b) Photoperiodism – The effect of daily light or day length on the flowering & fruiting of the plants is called as photoperiodism. The term photoperiodism was first used by Garner & Allard (1920). On the basis of daily light required for flowering, the plants are of three types-

• Long day plants (LDP)
• Short day plants (SDP)
• Dav natural plants (DNP)

On the basis of requirement of light, the plants are of two types

1. Photophilous or Heliphelous or Heliophytes –
   The plants which need bright light to grow. Examples – Sun flower, Ameranthus, Populus etc.
2. Sciophilous or Sciophytes –
   The plants which grow in less light or shadow.
   synthesis of anthocyanin pigment in plants. The purple sulphur bacteria use infra red & UV radiations for photosynthesis.