Different pollen sources can influence the
size and shape of the seeds (‘‘xenia’’ effect).
Pollen also can have a ‘‘metaxenia’’ effect,
influencing the tissue outside the embryo and
endosperm (Nixon, 1934, 1936; Reuveni,
1986). As an example of metaxenic effects
in date palms, Nixon (1934) reported that
‘Fard No. 4’ consistently produced earlier but
smaller fruit than the average of all pollen
sources studied, whereas ‘Mosque’ consistently
produced larger but later fruit than the
average. Pollination with pollen from different
Phoenix species also exhibited metaxenic
effects (Nixon, 1936). Although similar
effects have been reported from various other
countries, in some cases no observable
effects were reported from pollinations with
pollen from different males tested. This has
been attributed to the fact that metaxenic
effects are less pronounced when climatic
conditions are favorable (i.e., higher heat
units) or the possibility that the specific males
tested did not produce metaxenic effects
(Reuveni, 1986).