"He completed at least 18 paintings in 1889 of 'venerable, gnarled olive trees,' pervasive throughout southern France, of which he wrote: '"The effect of daylight and the sky means there are endless subjects to be found in olive trees. For myself I look for the contrasting effects in the foliage, which changes with the tones of the sky. At times, when the tree bares its pale blossoms and big blue flies, emerald fruit beetles and..." https://en.wikipedia.org/wiki/Olive_Trees_%28Van_Gogh_series%29