Tomato seeds that have been dried, imbibed and redried (primed) develop internal free space between the embryo and endosperm. Seeds of the ABA-deficient sitiens(sitw) tomato mutant can exhibit internal free space at the completion of seed development even without priming. Both primed and sitwseeds germinate more rapidly than untreated wild-type seeds. To determine whether internal anatomy predicts germination physiology, individual sitwand primed wild-type seeds were sorted into three categories based upon the extent of internal free space observed non-destructively using X-radiography. Category 3 (C3, extensive free space present) sitw seeds completed germination more rapidly than all other seed categories and genotypes in water, in abscisic acid (ABA) or under far-red illumination. The force necessary to puncture the endosperm caps (and testa) of C3 sitw seeds was less, and the percentage of nuclei in C3 sitw radicle tips in the G2 stage of the cell cycle was greater than for all other seed categories. Wild-type seeds exhibited free space following long-term priming, but germination was still prevented by far-red light and ABA, and endosperm cap strength and nuclear DNA contents were not altered. Endo-β-mannanase activity of individual endosperm caps was not consistently related to their resistance to puncture. While internal free space is diagnostic for primed tomato seeds and occurs in a fraction of sitw seeds, it is not predictive of many aspects of germination physiology.