An alternative to the cold test for maize, based on mean just germination (JG) time, when the radicle first appears (MJGT) and mean germination (G) time, when the radicle reaches 2mm (MGT), has previously been significantly related to seed lot performance in soil. MJGT and MGT are the mean lag periods between the start of imbibition and germination for JG and G respectively. The objectives in this paper were to ascertain whether the length of the lag period relates to and determines seedling size and variation, both within and between lots and if it can be reduced by a hydration / drying back treatment. Ten commercial lots of maize were germinated in moist rolled towels at 20°C and observed every 6h for 6 days and the time when each seed reached JG and G noted. The MJGT and MGT, that is the lag periods, were significantly related to differences in vigour, measured as mean shoot length (p≤ 0.001) and variation in shoot length after 6 days. Hydrating seeds of four lots, followed by drying back, significantly reduced the lag period and increased shoot length. The lag periods of individual seeds within the 10 lots were significantly (p≤ 0.001) negatively correlated with shoot length, suggesting that the source of variation in shoot length was the timing of germination and the duration of the subsequent growth period to measurement. The progress curves of shoot growth for lower vigour lots over this period entered the exponential phase later than the earlier germinating lots. For one lot, groups of seed that reaches G at 42, 48 and 52 h had similar growth curves when differences in time to G were eliminated by relating growth to time from G rather than from time set to germinate. Evidence here and in the literature suggest that vigour differences between seed lots of maize result from deterioration, leading to longer lag periods to allow for metabolic repair in physiologically older seed and that the delay in germination in lower vigour seeds reduces the time for seedling growth. The relevance of this hypothesis to seed vigour studies in general is discussed.