The differences occur in pollen and pollen tube morphology, development and cell composition (Yatomi, et al., 2002; Fernando, et al., 2005; Williams, 2008), spenn delivery (zooidogamy and siphonogamy
) (Norstog, 1977) and the duration of pollen germination and fertilization (Chamberlain, 1935; Donaldson & Bosenberg, 1995; Norstog & Nicholls, 1997).
In both groups pollen germinates to produce a pollen tube, responsible for delivering the male gametes (either motile, in cycads and Ginkgo, or otherwise non-motile) to the female gametophyte in the process of siphonogamy. In flowering plants the pollen tube can travel a long distance leading to extended siphonogamy.
Extended siphonogamy; Araucariaceae, Tsuga, Saxagothaea.
Callose deposits in pollen tubes: an apparent necessity for extended siphonogamy, because it compartmentalizes the male gamete apparatus.