The origins of pollen embryogenesis are still in doubt. Totipotency of
plant cells has traditionally been put forward as an explanation for
this phenomenon but we have found this interpretation to involve some
shortcomings. The pollen grain is a highly differentiated structure wh
ich should have a very reduced capability of regenerating a whole plan
t, whereas in some species the induction of androgenesis appears to oc
cur with greater facility than somatic embryogenesis. Furthermore, som
e microspores seem to have a tendency to morphogenesis and organogenes
is; spontaneous androgenesis occurs naturally in various species and m
any examples also occur of pollen dimorphism. Totipotency would seem t
o be insufficient to explain androgenesis and we propose that its orig
in might be found in the phenomenon of atavism. According to studies p
ublished on ancestral precursors of pollen, these structures appear to
have had high proliferation capacity. The ability to form a multicell
ular structure from a single haploid cell is shared by the meiocytes o
f ancestral algae, of the first land plants, and of present-day ferns,
which are evolutionarily related to pollen. Atavism is only expressed
under certain circumstances, as indeed is androgenesis, normally as a
consequence of an environmental stress. Out conclusion is that there
is evidence enough to suggest that androgenesis may well be the expres
sion of archaic genes of meiocytes with morphogenic capacity which wer
e naturally expressed in the ancestors of flowering plants.