Some parts of the inland scrubveld in South Africa may appear grey all the time to the occasional visitor not spending much time here. This is what a patch of Montagu veld looked like in March.

The greyness is intensified at times of drought and extreme temperatures when plant metabolism slows down. Too hot or too cold conditions reduce the rate of photosynthesis in the cyclic off-seasons.

Too little light will also reduce photosynthesis, as will too much carbon dioxide in the air. Both these factors are still unlikely as major causes of induced rest periods in plants of the open Karoo landscape.

Toxic air pollution will slow down photosynthesis. Let’s hope that stays away. Better, let’s ensure that stays away (www.bbc.co.uk).