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F Fi ig gu ur re e 1 1 The effects of ultradry storage on Eucommia seeds. No difference in viability or vigour was evident in seeds stored for two years either at ambient temperature after ultradrying or at low temperature. a a, , Ultradried seeds stored at ambient temperature: moisture content (m.c.) was 3.3%, germination was 97%, vigour index was 26.7. b b, , Seeds stored under conventional conditions at -20 °C: m.c. was 8.4%, germination was 96%, vigour index was 24. 1. c c, , Control stored at ambient temperature: m.c. was 7.5%, viability was lost.

The forces required to puncture intact lettuce (Lactuca satva) seed and pericarp, endosperm and embryo were measured by the Instron Universal Testing Machine. It required about 0.6 newton to puncture the endosperm in seeds imbibed in the dark at 6, 12 and 24 hours. Endosperm of seeds imbibed in the light or in dark with gibberellic acid required about 4.2 newtons at 6 and at 12 hours and only about 0.15 newton at 24 hours. Forces required to puncture embryo at all treatments and times remained constant at about 0.3 newton. Changes in the strength of the endosperm do not appear to be related directly to protrusion of the radicle.The dark dormancy of Grand Rapids lettuce seeds can be broken by light, GA, or fusicoccin (1, 9, 12). Ikuma and Thimann (7) concluded that the integrity of the endosperm determined the photosensitivity of the seed. Experiments involving mechanical removal of various parts of the seed covering and the microscopic observation (8) indicated that the endosperm was responsible for the restriction of embryo growth (4, 6). As injection of hydrolytic enzymes such as pectinase and cellulase promoted dark germination, Ikuma and Thimann (7) proposed that the final step in the germination control process might be the production of such enzymes. Lang and his colleagues (14,16) further verified that endosperm restricted embryo growth. Nabors and Lang (14) attempted to determine the force required to puncture the seed coats by means of changes in osmotic potential of the red-light-treated embryo. However, these workers used a rather crude means to puncture the empty endosperm seed coat derived from the darkimbibed seeds.The Instron Universal Testing Machine3 has often been used for measuring various textural characteristics of foods, and the puncture force determined by this instrument is regarded as highly objective (2). In the present study this machine was adapted to determine the relative strengths of the coverings (pericarp, endosperm) by measuring the forces required to puncture the intact seed, the seed minus the pericarp, and the excised embryo at various stages of imbibition and growth. We hoped that such a study might reveal the physiological significance of the seed coverings and their involvement in regulation of germination. cm/min, respectively. In each treatment 10 different seeds or seeds minus coverings were punctured individually and the puncture force recorded. RESULTS Force peaks from puncture tests on single lettuce seeds imbibed in the light for 12 hr are shown in Figure 1. Although some variation occurred among individual lettuce seeds, these were small compared to that reported for cooked dry beans (2). The force required to puncture an intact seed (pericarp + endosperm + embryo) was consistently higher than that required for puncturing a seed without the pericarp (endosperm + embryo). The difference between the two means gave a good indication of the strength of the lettuce seed pericarp. Similarly, the puncture force for the seed without the pericarp was consistently ...

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