(2) C.B. Van Niel, proposed  that the oxygen produced during the photosynthesis comes from water and not carbon dioxide. 

(3) Joseph Priestly  reported that green plants purify the air and restore to the air whateever the burning of candle or breathing animals remove from the air.  

Heliophytes : The plants that thrive in area where intensity of light is more are called  heliophytes e.g. Dalbergia.

Sciophytes : The sciophytes need less intensity of light and they grow under the canopy of trees. These plants have less amount of chlorophyll and remain smaller due to decreased rate of photosynthesis e.g. Oxalis.

Affect of CO₂ on photosynthesis : Carbon dioxide acts as a major limitin factor for photosynhesis. The CO₂ is 0.03 % in atmosphere and increase in amount of CO₂ upto 0.05% in atmosphere increases the rate of photosynthesis. Beyond it the rate declines. It is due to the increase in the temperature.

The C₃ and C₄ plants responds differently o the CO₂ concentration. The C₃ plants respond to a higher concentration of CO₂ by showing increased rates of photosynthesis while the C₄ plants saturate at low level of CO₂ and do not show increase in the rate of photosynthesis. 

Saturation point is the maximum intensity of light at which the rate of photosynthesis is maximum. Above this value of light intensity, rate of photosynthesis decreases.

Value : It is 60–70% for C₃ plants and about 200% of full sunlight for C₄ plants.