The need to conserve plant genetic resources can no longer be in doubt. The destruction of natural habitats, the replacement of multiple cropping systems with monocultures, the replacement of traditional varieties with uniform high-yielding cultivars all lead to genetic erosion and the loss of crop and plant diversity. Genetic resources are vital for crop breeding programmes as sources of new genes for, for example, disease and pest resistance. They are also vital as sources of pharmaceutical and novel industrial and food products. In their own right they may have potential as new crops.

Openings are present on the inside surface of the endosperm cell wall adjacent to the developing cotyledon. The objective of this study was to determine if the openings were present during seed growth, maturation and imbibition by observing the inside surface of the endosperm with low temperature scanning electron microscopy. The openings were found to be present throughout seed development, maturation and imbibition. The openings were not formed by attachment to the cotyledon surface. However, the inner surface of the endosperm was occasionally attached to the surface of the embryo. At seed maturity, outgrowths on the cotyledon cell wall surface were embedded in the cell wall of the inside surface of the endosperm. These structures were also observed in the imbibing seed. These points of contact between the endosperm and embryo of soybean seeds may align the embryo, endosperm and seed coat during growth, desiccation and imbibition.

Intact grains of barley (Hordeum distichum cv. Triumph) germinated rapidly in the dark or when exposed to brief daily light breaks in the temperature range 15–25°C, although germination proceeded less rapidly at low temperatures. Prolonged illumination (16 h/day) or continuous light inhibited germination of grains most effectively when conditions were less than optimal for germination, i.e. under low temperatures, restricted water, and low water potential induced by mannitol. Embryos isolated from grains responded in a similar way to light applied when the amount of water was restricted; water stress did not affect germination percentages in the dark or after one brief light break (3 min) but appreciably reduced the rate of germination. While light was only slightly inhibitory to embryos under optimal germination conditions, its inhibitory effect was intensified when other factors tending to delay germination were present. Water restriction also caused ABA contents in embryos to rise. Under conditions of water stress (water restriction or low osmotic potential), CaCl2 enhanced the inhibitory effect of light; however, addition of LaCl3 reversed this effect. The nature of light-induced inhibition of germination is discussed.

Germinability and the rate of germination were related to seed mass in Lithospermum arvense L. and Anchusa arvensis (L.) Bieb. Prior to germination experiments, seeds from two populations of each species had been sorted into nine similarly sized groups according to their seed mass. Germinability varied greatly among the different seed-mass fractions in L. arvense, while differences were smaller in A. arvensis. Germination rate varied with seed mass in some cases. However, in many cases where clear patterns in the relationship between germination characteristics and seed mass were found, these patterns differed both between species and between populations. Furthermore, the character of the relationship varied depending on the experimental conditions used. It is hard to identify the cause of these relations since within- and between-plant variability can affect both seed mass and germination characteristics independently. It is concluded that the results of a germination test can differ depending on the seed mass fractions used, but that the magnitude and direction of such differences are difficult to foresee. Therefore, seed batches should be prepared with care, and experiments designed with awareness of the importance of the germination conditions chosen.