Position of the caryopsis on the parent plant

In the grasses the term ‘seed’ is commonly used to describe the dispersal unit. However in some cases the dispersal unit may be a spikelet, a floret, or a naked caryopsis. In addition the term ‘grain’ is frequently substituted for the word caryopsis, particularly among the cereal grasses. In the context of this chapter on structure the term grain will be used as the general descriptor for the fruit. To some extent the terms seed and grain will be used interchangeably, except where clarity in the separation of anatomical structures is of significance.

Example of Avena fatua:

The inflorescence in Avena fatua is a determinate panicle that matures basipetally but the spikelets mature acropetally (Green & Helgeson, 1957; Raju & Ramaswamy, 1983; Raju, Jones & Ledingham, 1985) (Fig. 2.1). Self–pollination is the rule and the florets are chasmogamous (Raju et al, 1985). Some outcrossing has been observed ranging from one to twelve per cent (Imam & Allard, 1965). Dormancy is present in the grains at an early stage: excised caryopses can germinate as early as three days after anthesis (Morrow & Gealy, 1983) yet by 15 days, dormancy is present and increases up to seed maturation (Thurston, 1957a). The degree of dormancy can vary with position of the spikelet on the panicle (Anghel & Raianu, 1959); grains at the bottom of the panicle are more dormant than those at the top (Schwendiman & Shands, 1943).