The decrease of relative humidity from 80 to 50% makes it
possible to reduce growth but does not modify the phyllochron
or the plastochron. However, we know that a considerable
decrease in growth, without modification of the plastochron,
leads to bud formation and a possible initiation of flowering
(Galopin and Guerin, 2002). If the trophic hypothesis of the
effect of relative humidity on growth is retained (Schu¨ssler,
1995), a value of less than 50% could then lead to a lengthening
of the phyllochron, a halt in the appearance of new pairs of
leaves and bud formation.