Today when Venus passes across the face of the Sun, we should remember that our original atmosphere consisted of nitrogen and carbon dioxide. Free oxygen is something that is not really chemically possible. Yet we have it as a result of plant life busily photosynthesising and converting carbon dioxide into oxygen during daylight hours. This is the original use of solar energy!

Plants require carbon dioxide to grow and why not help them by increasing the level of carbon dioxide? Normally, this is something that is undesirable, since carbon dioxide is the original greenhouse gas, as our neighbouring planet Venus can testify. But in a controlled, genuine greenhouse environment, there is no real reason why the level of carbon dioxide should not be enhanced in some way.

Carbon dioxide is essential, however, since high concnetrations of carbon dioxide can lead to dizziness or even unconciousness of the personnel. Some plants will require higher levels of nutrients to compensate for some of the changes that occur. Particularly tomatoes and violets are sensitive to increased levels of carbon dioxide, hence the need for constant monitoring of the ambient concentration.