Seedcoat Structure in Coronilla varia and its Relations to Hard Seed1

Hard seeds are common in some seedlots of crownvetch (Coronilla varia L.); such seeds are impermeable to water and require scarification before planting. However, unless carefully performed, scarification can lead to seedcoat injury with consequent loss of vigor and germinability. To locate the region or regions responsible for impermetability in ‘Penngift’ crownvetch, sized and known hard seeds were pierced to known depths and subsequently tested for imbibition of water and germination. All seeds punctured to a depth of 98 μm or more germinated rapidly while only 5% of those punctured to a depth of 47 μam or less subsequently germinated. Measurements of cross sections of crownvetch seeds indicated that the macrosclerid cells extended to a mean depth of 45 to 50 μm. In addition, an inner integument at an average depth of 73 μm also had to be pierced before germination occurred. Colors developed after staining with safranin and fast green indicated that the cuticle, macrosclerids and inner integument were lignified. Extensive deposits of tannin‐like materials were noted just below the inner integument.