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Effect of Chemical and Physical Treatment on Hard Seed of Penngift Crownvetch¹

Various chemical and physical treatments were applied to hard seed of "Penngift" crownvetch, Coronilla varia L., in an attempt to make such seed permeable to water. Soaking for periods of up to 24 hours in acetone, benzene, chloroform, hexane, petroleum ether, anhydrous ether, ethyl alcohol, and t-butyl alcohol had only slight effects on hard seed. However, the percentage of rotted seed increased. Treatment with enzymes such as hemicellulase and pectinase was likewise of slight value. Alternate freezing and thawing at temperatures as low as –80 C and dry heat treatment at 75 C had little effect on reducing the number of hard seed. Treatment with infrared heat lamps at temperatures of 85 to 100 C reduced hard seed content slightly but increased the percentage of rotted and firm seed appreciably. Treatment of 19 seed lots of Penngift crownvetch with sulfuric acid (18 N) for 15 min (with agitation) reduced hard seed from an average of 60% in the control to 11% in acid treated seed and increased readily germinable seed from 16% in the control to 75%. For the same lots, treatment in liquid N (two 2-min dips separated by a l-min interval) reduced hard seed to 15% and increased readily germinable seed to 65%. Treatment in ,boiling water (15 sec with agitation) reduced hard seed to 27% and increased readily germinable seed to 47%. Mechanical scarification reduced hard seed content to 4% and increased readily germinable seed to 78%. Scanning electron micrographs of seed scarified by either acid or mechanical means indicated that lumens of the macrosclereid cells were exposed, permitting imbibition of water. Seed subjected to differential thermal expansion in boiling water or liquid N had fissures penetrating the macrosclereid layer.

² Respectively, Research Aid, Professor, and Associate Professor, Department of Agronomy, The Pennsylvania State University, University Park, Pa. 16802.

Received for publication December 6, 1969.