Abstract:
1. The chlorophyll-content of Bechuanaland grasses is not constant throughout the year, but varies from a very high initial value on young leaves, decreases according to the duration and intensity of drought periods, and increases again after rains.
2. Even during periods of twenty-four hours the chlorophyll-content varies greatly, decreasing from early morning to midday, and increasing again during the ensuing night. Decrease and increase depend upon meteorological factors ot the moment, so that on rainy days the variation lies within a few per cent., but on extremely dry and sunny days may extend to 30 per cent.
3. High nocturnal temperature favours a higher general chlorophyll-content throughout the day. Low nocturnal temperature is associated with low chlorophyll, even although the soil moisture is adequate. In both cases, however, chlorophyll destruction and chlorophyll synthesis are regarded as occurring concurrently, the actual content at any time representing the equilibrium between the two processes.
4. The values found in 1923-24 were higher than those found in 1924-25 owing to differences in nocturnal temperature in the two seasons. In the 1923 growing season the chlorophyll-content of the grasses of the Vryburg District was higher than that of European grasses; in the 1924 season about the same, or rather lower. Since the average chlorophyll-content is different in the two seasons, the data cannot be directly compared. What is termed a low value for 1923 would be high for 1924. Apart from nocturnal temperature, other factors, as yet uninvestigated, may play a role.
