Intra‐population variations of several characteristics related to fertility were assessed for a nature‐reserve population of Primula sieboldii in the flood plain of the Arakawa River. Although there were large intra‐ and inter‐clonal variations of fruit and seed sets as well as other female fertility components in the 13 clones examined, female fertility was generally low, except in a homomorph clone. Pollinator availability was assessed by continuous monitoring of insect visits with 8 mm film. No insect visits were recorded during the monitoring of total 68 flowers over 16 hours in the nature‐reserve population. In contrast, a high pollinator visitation rate was recorded in a reference population of P. sieboldii on the flank of Mt. Yatugatake. Thus, the low rates of seed production in the nature reserve was due to a shortage of compatible pollens as a result of the limitation of pollinator availability. Stigmas of flowers in various clones occasionally were loaded with pollen grains whose sizes were not significantly different from those of anther pollens of the same flowers. However, pollen germination on stigmas was observed only in the flowers of a homo‐morph clone whose flowers have pin‐type stigmas and anthers with compatible thrum‐type pollens at the same height. Exceptionally high fertility of the homo‐morph clone would be associated with its inbreeding habit.

growth of ducksalad (Dilday et al., 1994), which is a major weed in the southern USA and causes a 21%The allelopathic effect of rice (Oryza sativa L.) on lettuce (Lactuca reduction in the yields of direct-seeded rice (Smith, sativa L.) and ducksalad [Heteranthera limosa (Sw.) Willd.] was investigated with water soluble extracts. Ducksalad is a major weed 1988). In field experiments, some rice cultivars produced in southern USA rice fields. 'PI312777' and 'Rexmont', which are a weed-free radius of 10 to 15 cm around an individual suppressive and nonsuppressive to ducksalad in the field, were used plant while nonsuppressive cultivars were densely surto establish the bioassay of allelopathic activity in rice. Water soluble rounded by ducksalad. Rice cultivars with an allelocompounds, which were extracted from rice seedlings and adult plants, pathic effect to barnyardgrass (Echinochloa crus-galli were applied to lettuce seeds. Leaf extract of PI312777 inhibited the (L.) Beauv.) were also screened by assessment in the root growth of lettuce more strongly than those of Rexmont. Extracts field and laboratory (Olofsdotter and Navarez, 1996). from the leaves of rice seedlings at the six-leaf stage inhibited the Varietal differences in the allelopathic effect were degrowth of ducksalad and lettuce, and a close relationship existed tected using the plant box method, in which lettuce between the inhibitory effect and the two test plants. A wide range seeds were placed together with rice seedlings in agar of variation in allelopathic activity among rice cultivars was assessed using water soluble extracts from their leaves and lettuce as a test plant.

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