The genus Cinnamomum

46 P.N. Ravindran et al.
male phase on the next morning. Interplanting of (a) and (b) types can therefore ensure
outcrossing in avocado. The situation is very similar in Cinnamomum as shown by the
studies by Joseph (1981) and Kubitzski and Kurz (1984). The latter workers investigated
C. verum and C. camphora and confirmed the observations detailed above.
They used the term synchronised dichogamy for the situation existing in the genus
(Fig. 2.12b).
The type (a) plant is essentially female in the FN of the first day and male in the AN
of the following day. Type (b) plant is functionally female in the N/AN of the first day,
and male in the FN of the following day. Both (a) and (b) plants occur mixed in any
natural population and hence large numbers of functional male and female flowers are
available for any given day. Because of the temporal separation, within-flower pollination
(autogamy) as well as between-flower pollination (allogamy) are prevented,
leaving between-tree pollination as the only alternative. According to Kubitzski and
Kurz (1984) this is the basic floral behaviour in the family. This view is supported by
the fact that this phenomenon occurs in all tribes and in both new and old world
species. Protogynous (or synchronised) dichogamy is evolved as an adaptation for
outcrossing and is the forerunner of dioecy, the obligatory outbreeding mechanism
(present in some taxa in Lauraceae).
No research has so far gone into the physiology of dichogamy in cinnamon. However,
the studies by Sedgley (1977) on avocado (Lauraceae) shed some light. Pollination of
the female phase flower results in fertilisation and fruit set. Pollination of the male
stage flower results in some pollen tube growth, but the growth is arrested in the lower
style and the tube does not reach the ovary or fertilise the ovule. This inhibition is
correlated with an increase in callose (a -1,3-glucan cell wall component). The thickening
of the cell walls of the stylar tissue may prevent or reduce the availability of
nutrients to the pollen tube, thereby preventing its sustained growth. The existence of
two flowering types within the same species may have a complicated physiology and
may be genetically determined. Sedgley (1985) has shown that in avocado the opening
of flowers is related to light and dark periods.
Mohanakumar et al. (1985) in a preliminary study reported that the anthesis
commenced at around 9:00 am, continued until 1:00 pm and reached a peak at between
11:00 am and 12:00 noon. After 1:00 pm anthesis came to an end. Anther dehiscence
began by 11:00 am and continued up to 2:00 pm. Pollen grains are spherical, the equatorial
diameter is about 23.4 m. Stainability is around 96.8% (in 0.5% acetocarmine).
The highest germination as well as tube growth is in 35% sucrose solution (53.7% and
tube length 46.8–78 m). Pollen grains are binucleate (Erdtman, 1952; Brewbaker,
1967). Cinnamon flowers are insect pollinated. Mohanakumar et al. (1985) reported 13
insect pollinators on cinnamon, but nothing is known about their relative efficiency.
Honey bees (Apis cerana, A. dorsata and A. corea) are the most active as they are noted
most often on blooming cinnamon trees.
Floral anatomy
The floral anatomy of Cinnamomum iners was studied by Sastri (1952). Shylaja (1984)
studied the floral anatomy of C. verum and found that the floral anatomical features are
very similar to those of C. iners. In C. verum the vascular supply of the pedicel consists
of a closed ring of vascular bundles, which show secondary thickening to some extent.
At its base the closed ring is triangular in shape from which six prominent traces