HIGH PRESSURE AND SEED GERMINATION

Abstract

This paper deals primarily with the direct application of high pressure to seeds. Certain physico-chemical effects of high pressure have been discussed in an earlier paper (Davies, 4). De Vries (3), using rather low pressures (6 to 8 atmospheres) for a period of 2 to 3 days, found in one species, Oenothera Cockerelli, that only a 2 percent germination was obtained in 5 days before applying the pressure, while after applying the pressure a 72-percent germination was obtained in 3 days. Bulgia (i), working with caryopses of Hordeum vulgare, found that reduced oxygen pressure retarded the activity of the caryopses; while Morinaga (7, 8), with seeds of Trifolium repens and Typha latifolia, found an increased germination under reduced oxygen pressure. The present study deals with the application of high pressure to seeds of Medicago sativa (alfalfa) and Melilotus alba (sweet clover). The delay or failure to germinate in the two species studied is due entirely to the seed: coat, for when the impermeable nature of the seed-coat is destroyed either by the application of hydraulic pressure or by other mechanical means, the seeds germinate readily. There are two mechanical methods already in use by which the percentage germination of seeds may be increased: first, by scarification, through the blowing of the seeds against coarse sandpaper or some other abrasive; and secondly, by the use of a strong corrosive such as concentrated sulfuric acid. Harrington (5) reports very favorably on the practice of scarification, but Nelson (g) says that with the larger types of seeds (red clover), although the percentage of hard seeds is reduced, the increased number of broken seedlings results in a total germination as low as the untreated seeds or lower. Concentrated sulfuric acid has been used by many workers to increase the percentage germination of hard-coated seeds. Love and Leighty (6) found with the seeds of Melilotus alba that treatments from 25 minutes to an hour resulted in good germination tests, but that a treatment for 2 hours resulted in injury to the seeds. Coe and Martin (2) obtained a good germination test from the seeds of Melilotus alba after I5 minutes treatment with the acid. For the application of high pressure to be advantageous, the seeds must retain the possibility of a high percentage of germination after being dried