Tobe & Raven, Embryology of Onagraceae (Myrtales) 
677 
Figs 19-22. Longitudinal sections of ovules and seeds in various stages of development, showing 
general embryological features in older embryo sacs and nucelli. 19. Ovule with two-nucleate 
embryo sac (photo from Gaum miitabilis). Note two nuclei positioned on micropylar side. 
20. Ovule with organized embryo sac composed of an egg apparatus (eg) and a single polar 
nucleus (pn); arrowheads indicate scattered starch grains in nucellus (photo from Fuchsia mdicans). 
21. Ovule with embryo sac just fertilized showing porogamy (photo from Gayophytum 
ramosissiniuni). See pollen tube (pol) penetrating into the nucellus on micropylar side. 22. Seed 
with embryo sac containing free endosperm nucleus (fe) and a globular proembryo (pern) 
(photo from Clarkia heterandra). All scales equal 50 pm. 
