Growth and flowering of cacao under controlled atmospheric relative humidities

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Abstract
Young clonal cacao trees have been grown for 390 days in controlled environment rooms, either continuously at relative humidity levels of 50–60% (low), 70–80% (medium) or 90–95% (high), or alternated between any two of these levels at 109-day intervals. The temperature was 80 ± 1 °F. (26·7 °C.) throughout, and the plants were watered frequently to keep the soil near to field capacity. Plants at the low humidity flushed before the others, but thereafter the period between flushes was rather longer at low and medium than at high humidity. There was little difference in numbers of leaves expanded, but the area of each expanded leaf was consistently least during periods of high humidity and, overall, greatest during periods of low humidity. Leaf weight per unit area was greatest at high humidity. Total dry weight increase per plant was greatest under alternating humidities, particularly when one of the periods was at high humidity. At constant high humidity both net leaf area and total dry weight were least of all. Stem length was significantly greater at high humidity than at low. Flowering was good in all treatments and usually ‘particularly profuse following the transfer of plants from a low or medium to a high humidity.

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