Germination studies indicated that increasing priming duration (-1.0 MPa at 20 °C for 7, 14, or 21 days) increased `Moss Curled' parsley [Petroselinum crispum (Mill.) Nyman ex A.W. Hill] germination rate quadratically and seed moisture content linearly. A histological and anatomical study was conducted to identify and/or quantify principle mericarp organ or tissue volume changes influenced by priming duration. Embryo volume increased as priming duration increased from 7 to 21 days (0.014 to 0.034 mm3), and this was due more to radicle (0.007 to 0.022 mm3) than to cotyledon (0.006 to 0.011 mm3) growth. Concomitant with increased embryo volume was increased volume of the depleted layer (space formation, surrounding the embryo), from 0.038 after 7 days to 0.071 mm3 after 21 days, and increased hydrolysis of central endosperm (a thick-walled endosperm type). In nonprimed mericarps, central endosperm cells constituted 97% of the endosperm volume. The remaining 3% was comprised of 1% depleted layer and 2% distal endosperm (small, thin-walled, and irregularly shaped endosperm cells). During 7 or 21 days of priming, ≈10% or 40%, respectively, of central endosperm cells were hydrolyzed centrifugally around the embryo with a corresponding decrease in volume of central endosperm with thick cell walls. In addition, distal endosperm cells adjacent to the depleted layer, containing reserve materials, were digested of contents following 21 days priming, and sometimes, following 7 days priming. A long priming duration resulted in degradation of pericarp tissues, as indicated visually and by a decline in pericarp volume. We hypothesize that priming duration of parsley primarily influences radicle growth and centrifugal digestion and utilization of central and distal endosperm, resulting in a larger depleted layer required for embryo volume increases. Secondary events influenced by priming duration include cotyledon growth and degradation of pericarp tissues.
`Moss Curled' parsley [Petroselinum crispum (Mill.) Nyman ex. A.W. Hill] schizocarps were osmotically primed in polyethylene glycol at -1.0 MPa for 7 days at 20 °C. The smaller of the two mericarps within a parsley schizocarp had lower germination percentage, but similar rate and synchrony of germination. Osmotic priming increased germination percentage, rate, and synchrony, irrespective of mericarp half. This promotive effect of priming on germination was associated with embryonic advancement as indicated by a doubling of radicle and cotyledon volumes, without changes in lengths of these organs. Periclinal divisions of the lateral expansion meristem, distinct in primed radicles but indistinct in nonprimed radicles, led to radial alignment of the cortical cells and a doubling of cortical volume and thereby increased radicle volume. Each embryonic cotyledon of primed mericarps had three distinct procambial bundles that differentiated along most of the cotyledon length, while nonprimed cotyledons had from zero to three that differentiated only a short way into the cotyledon. Priming increased coyledonary procambium length by 5-fold and volume by 11-fold. Increased embryonic growth due to priming was associated with greater endosperm depletion adjacent to the embryo. The schizocarps frequently separated or partially separated into component mericarps during priming, indicating a weakening of pericarp tissue along the commissural suture and possibly elsewhere.