Longspine sandbur germinated readily after 3 months of storage at 0 to 4 C. Germination was 15 to 82 and 10 to 76% for seed retained by or that passed through a 1.7-mm-mesh screen, respectively, and was greatest in complete darkness near 30 C. Light inhibited seed germination at most of the temperatures tested. Incubating imbibed seed at 40 C and 40/10 C for 3 weeks reduced the viability of seed that did not germinate by more than 50%. Primary seed within the bur germinated 77% and secondary seed germinated 35% during 2 weeks at 35/10 C (16 light/8 dark h). Primary seed placed in polyethylene glycol (PEG) solutions ranging from −0.5 to −1.5 kPa water potential germinated as much or greater than seed placed in water, while secondary seed germination was inhibited by similar osmotic potentials. Seedlings emerged from depths to 11 cm but emerged most readily from 1- to 3-cm depths.

Experiments were conducted to investigate the effects of shading on and location of the mother plant on germination and hormone content of Palmer amaranth seed. Increasing the shading from 0 to 87% decreased germination of fresh, viable seeds in dark from 25 to 12%. Abscisic acid (ABA) content of seeds from plants in 0% shade increased from 13.3 ng g−1 dry seed to 19.1 ng g−1 dry seed with 87% shade. Shading of the mother plant did not influence the 1,000-seed weight of Palmer amaranth. Seeds that matured in the top and middle third of the mother plant had 67 to 78% greater germination than those that matured in the bottom third of the mother plant. Endogenous gibberellic acid (GA) content of seeds did not differ between locations on the mother plant; however, the ABA content of seeds produced on the bottom third of the plant was 46 and 59% higher than the ABA content of seeds produced at the middle and top third of the plant, respectively. Endogenous ABA or GA content of seeds and 1,000-seed weight had no relationship with seed germination over and above the treatment effects. This research suggests that shading and plant location can influence germination of fresh, viable seeds of Palmer amaranth, which will be a dormancy strategy for seed dispersal over time.

The performance of cucumber (Cucumis sativus L.) seeds in relation to ovary and ovule position was monitored during seed production. Seeds from three (first, seventh and tenth nodes) fruit positions and three (stylar, intermediate and peduncular) ovule positions were harvested serially during development and characterized with physiological and cellular markers. Seed moisture contents declined to 30%approx. 35 d after pollination (DAP) and remained constant thereafter. At 42 DAP the maximum dry weight was acquired in seeds except those from peduncular segments, whose dry weight accumulation lagged behind. The onset of germinability and desiccation tolerance occurred before the attainment of maximum dry weight, whereas seed performance, as shown by laboratory germination and greenhouse emergence, was largely improved after the completion of seed development. Cell cycle activities (DNA per nucleus and β-tubulin content) ceased by 28 DAP, whereas the degradation of seed chlorophyll continued during the entire maturation period. Seeds from the top fruit and from the peduncular fruit segments were delayed in reaching maximum quality compared with seeds from other positions, and this was correlated with a slower decline of chlorophyll fluorescence.