The effect of relative humidity was studied at four levels (60%,
70%, 80% and 90%) in the DFT system over a period of 10 wk. The
results showed that the humidity did not affect shoot
multiplication significantly (Table 7). During the first 2 wk, the
height of the P. helferi plants cultured at the four levels of relative
humidity were not significantly different. However, by the trial end,
the P. helferi cultured at 90% humidity had grown to a height of
3.08 ± 0.22 cm whereas those grown at 60% humidity produced the
tallest plants at 6.15 ± 0.33 cm. This result was consistent with the
findings of Nelson et al. (2003) in which calcium uptake and its
accumulation in tulips was lower at high relative
humidity (82%) than in those reared at low humidity (42%).
However, in Hydrangea macrophylla culture, a decrease in the
relative humidity from 80% to 50% was reported to lead to a 38%
decrease in height. reported that the height of some foliage species from
warm and humid conditions increased when the humidity was
elevated.