The effects of culture medium rigidity on adventitious bud production and tissue vitrification in needle cultures of Sitka spruce [Picea sitchensis (Bong.) Carr.]

Adventitious bud formation on Sitka spruce [ Picca sitchensis (Bong.) Carr.] needle explants was strongly dependent upon the rigidity of the culture medium. In general, of organogenesis was greatest on weak gels and poorest on more rigid gels resulting from increased medium pH or agar strength. There was a significant interaction between agar strength and pH, with the optimum pH for organogenesis declining with increasing agar strength. Poor organogenesis at high agar concentrations was not due to toxic impurities since increased adventitious bud production could be stimulated by decreasing the medium pH whilst maintaining a high agar strength and an agar washing treatment had no significant effect. Although high levels of organogenesis could be sustained on weak gels the resultant adventitious shoots often showed severe vitrification. The frequency of shoots showing vitrification could be reduced by growing the tissues on harder media but this resulted in reduced shoot elongation. Vitrification of needle tissues did not stimulate the formation of adventitious buds in the absence of cytokinins.     

Behavioral Aspects of Rodent Population Biology

Five approaches to the study of behavior as a factor in thepopulation biology of rodents are outlined. These approachesare: (1) genetics, (2) physiology, (3) chronobiology,(4) behavioralecology and sociobiology, and (5) the use of intra- and inter-specificcomparisons. For each approach selected examples from the recentliterature, from this symposium and from my own work are usedto illustrate the new directions that are emerging for analyzingbehavior as a factor affecting natality, mortality and emigration/immigrationin rodents. Areas where additional investigations are neededare noted including some questions to be tested by future experiments.A variety of new techniques that have been developed or areinnovative applications of existing techniques are incorporatedinto the examples. Most of the material presented concerns fourgenera of rodents, Microtus, Mus, Peromyscus, and Rattus. Thefollowing major conclusions emerge from an overview of theseapproaches: Most recent research on behavior as a factor inrodent population biology has been concerned primarily withnatality. Few investigators have dealt with mortality and onlya limited number have explored emigration/immigration. Fieldand laboratory studies on behavioral aspects of rodent populationbiology have become more integrated than they were several decadesago. Both proximate and ultimate questions about behavior andpopulation dynamics are now being tested by both laboratoryand field methods. In contrast to some earlier approaches thatoften viewed population control as involving a single factor,most emerging conceptual frameworks have, as a major assumption,that population regulation is a multi-factorial process includingmany behavioral components.     

Duration of cereal aphid populations and the effects on wheat yield and breadmaking quality

Field-caged and open-plot populations of the aphid Sitobion avenae on winter wheat (cv. Maris Widgeon) were sampled approximately twice-weekly in the summer of 1978. Cage populations began at growth stage 10.2 (Feekes scale) (Zadoks, G. S. 52); they were removed by spraying with pirimicarb at growth stages 10.54 (71), 11.1–11.2 (77) and 11.2–11.3 (85) respectively. All cage populations reduced mean weight per grain but the effect per aphid unit was lowest in the population of longest duration. Although the aphid index in the open plots was higher than that in the early cage treatment, yield was unaffected. Cage infestations affected the breadmaking quality of the grain: percentage flour extraction was reduced and there was an increase in colour, nicotinic acid content and thiamine (vitamin B₁) content of the flour; percentage nitrogen in the flour was unaffected but there was a reduction in baking value and in the high molecular weight glutenin content; infestation also reduced α-amylase activity. Different aspects of grain quality did not change in parallel with one another or with yield changes and thus damage thresholds will vary according to the yield/quality measure under consideration.     

Structure and Process in the Interpretation of South American Myth: The Arawak Dog Spirit People

Recent work on oral narrative has emphasized differences in textual and performative approaches, which in turn has tended to widen the distinction between two fundamental categories of anthropological thought: structure and process. This paper argues that, at least for the interpretation of South American myth, an integrated approach is essential. After reviewing the epistemological basis of current problems in myth studies, the paper attempts a structural analysis of myths with the theme of a metamorphic conjugal union between human and nonhuman. Processual considerations are introduced in the form of syncretic myth, and the argument is advanced that there exist syncretic transformations of a structural nature. Identifying these provides the beginnings of a bridge between structure and process, and leads to an examination of the performative context of the subject myth. Other narrative genres, dealing with explicitly ethnic concepts, are implicated in the processual sequence of the telling and interpretation of the tale. The attempted synthesis of structure and process in narrative analysis leads to an engagement with two difficult problems: the relationship between ethnicity and kinship; and the transition from myth to history. [myth, structure, process, ethnicity, kinship]