REPRODUCTION
Embryology
The embryology of the neem described by Garudamma and Nair and Kanta. Garudamma
reported only a single layer of sporogenous tissue in the microsporangium. However, Nair
and Kanta noted two to four layers. The microspore mother cells undergo reduction division
almost simultaneously. Microspores are liberated by the degeneration of mucilaginous
sheath surrounding the. The tapetal cells are uninucleate to begin with but become 2-4
nucleate.
Some of the tapetal nuclei fuse to form polyploid nuclei. Pollen grains are shed at the
3-celled stage. The mature pollen grains are tri-or tetracolporate, prolate, spheroidal or sub
prolate. Apocolpium is medium and endocolpium la-longate and elliptical. Ora are circular.
The exine is 2 um thick, its surface is psilate in light microscope and scorbiculate in SEM
(personal communication by Dr. M. Chaturvedi) and that of the acetolysed grains is 55x39um
(47-64um x 35-39um). Generally the number of germinal furrows is four. However, it varies
from three to nine. A few cases of polyspory have been reported. It is recorded that pollen of
neem cause pollinosis is a low extent.
Pollen of neem are among the regularly supplied antigens to various allergy clinics in India,
where it finds use of both in diagnosis and treatment. Although neem is unlikely to be
anemophilous, the presence of pollen in air sample requires explanation. One of the
possible reasons for the presence of air-borne pollen could be the profusion of flowers,
heavy flower shedding and dry hot surface air currents in the flowering season.
The ovule is anatropous, bitegmic and
crassinucellate. Generally one cell develops
into megaspore mother cell out of a
multi-cellular, hypodermal archesporium.
The development of embryo sac is of the
Polygonum type. The antipodal cells
degenerate before fertilization. Twin and
triplet embryo sacs have also been reported.
The flowers are cross-pollinated and
fertilization is porogamous. Nair and Kanta
have described syngamy and triple fusion.
The endosperm nucleus divides before the
zygote. The endosperm is free nuclear and
later becomes cellular. In the mature seed
(for neem oil) only 3 to 5 layers of endosperm
tissue persist. Endosperm nodules are
reported as a rare occurrence.
The zygote divides by the laying down of a transverse or oblique wall. There is a statement
that further divisions are irregular, which in the opinion of the authors may be due to
non-availability of stages in early embryonic development. The mature embryo is
dicotyledonous. Cotyledons are plano-convex and collateral. Tricotyledony and polyembryony
are also reported in certain instances. The additional embryos are traced to the synergids.