J.G.C. Small

Seed germination in Citrullus lanatus. Part 1. Effect of white light and growth substances on germination

Germination of Citrullus lanatus seed is inhibited by white light. The nature of the light inhibition resembles that of a low-energy reaction. Removal of the outer seed structures, especially the membrane enveloping the embryo, overcomes the inhibitory effect of light. Gibberellic acid slightly reverses the inhibitory effect of light while kinetin and particularly ethrel strongly promote the germination of seed in white light.

A preliminary study on the germination of Sclerocarya birrea subsp. caffra

Seeds of Sclerocarya birrea (A. Rich.) Hochst. subsp. caffra (Sond.) Kokwaro, commonly known as marula, occur in locules within a hard lignified endocarp. The endocarp appears to restrict germination mainly by offering mechanical resistance. It may also restrict the leaching of germination inhibitors and possibly serve as a barrier to oxygen diffusion. The endocarp does not restrict water uptake. High germination counts were only obtained by removing opercula. Leaching slightly improved germination of seeds in intact endocarps. The optimum germination temperature of opercula-removed seeds was between 27° and 37°C. Storage improved rate of germination.

Seed germination in Citrullus lanatus. Part 2. The involvement of phytochrome and ethylene in controlling light sensitivity

The inhibitory effect of light on the germination of Citrullus lanatus seed shows the typical red — far-red photo-reversibility of a phytochrome mediated system. During the dark period following an inhibitory far-red light treatment a secondary skotodormancy develops. The inhibiting effect of light on germination can be effectively reversed by ethylene.

The effect of water stress on the germination of Citrullus lanatus seeds

The germination of Citrullus lanatus seeds is extremely sensitive to water stress. A decrease of 13,6 % in the total water content is sufficient for the complete inhibition of germination. Exposure of seeds to water stress at a very late stage of germination after normal incubation in water prevents radicle emergence. Prolonged water stress treatment does not induce secondary dormancy in these seeds. Water stress which completely inhibits germination does not appear to affect the conversion of phytochrome intermediates to Pfr or the photoreversibility of phytochrome during light treatments.

Seed germination in Citrullus lanatus. Part 4. The inhibition of germination within the fruits by light

The germination of Citrullus lanatus and Lactuca sativa cv. Grand Rapids seeds is inhibited in the light when covered with fruit shells of C. lanatus. This inhibition appears to be due to the light which penetrates the fruit shells. Studies on lettuce seed showed that the penetrating light is far-red rich. Although covering with fruit shells inhibits the germination of C. lanatus seeds in the light, high germination is obtained when such covered seeds are transferred to the dark. This is taken to indicate that the light penetrating the fruit shells is not monochromatic far-red light. This allows for the formation of phytochrome intermediates within the seeds, which in time could cause subsequent dark germination of C. lanatus seeds. The results obtained support the hypothesis that light contributes to the inhibition of germination of C. lanatus seeds within the fleshy fruits.

Seed germination in Citrullus lanatus. Part 3. The possibility of light as an inhibitory factor for germination of seeds within the fruits based on light measurement studies

The germination of Citrullus lanatus seed is under phytochrome control. The optical properties of the fruit of this species indicate that the quality and intensity of light which penetrates the fruit could be an important factor in the inhibition of seed germination within the fruit.

Die saadknop en aspekte van kieming by Crinum bulbispermum en C. macowanii

The ovule and aspects of germination in Crinum bulbispermum and C. macowanii. Apart from an integument primordium, integuments are lacking in the ovules of the studied species. The plants are self- as well as cross-pollinating. Naked embryos were found among well-developed seeds in the fruits. The seeds germinate spontaneously in dry containers. Although light has no effect on germination, it inhibits bulb formation in the seedlings.