Our understanding of the roles EFNs play in plant biology is being revolutionized with the use of new tools from developmental biology and genomics, new modes of analysis allowing hypothesis-testing in large-scale phylogenetic frameworks, and new levels of inquiry extending to community-scale interaction networks. But many central questions remain unanswered; indeed, many have not yet been asked. Thus, the EFN puzzle remains an intriguing challenge for the future.

Controversy exists as to whether the tropical shrub Guettarda scabra (Rubiaceae) is distylous. Variations in stigma and anther position and floral morphology of G. scabra were studied in a population in south Florida. Stigma and anther height have unimodal distributions, but stigma‐anther separation is bimodally distributed and can be used to identify a long‐styled and a short‐styled morph. Stigma width varies between morphs, but anther length, pollen diameter, and stigma papillae length do not. The morphs occur in a 1:1 ratio in the two populations studied. G. scabra is self‐compatible and can pollinate itself. Styles of the two morphs have similar relative growth rates in early development. Stylar growth is inhibited in the short‐styled morph when buds are approximately 12 mm long. Anther height differs between morphs because of different relative growth rates and because the long‐styled morph corolla tube, where the anthers are attached, stops growth before the tube of the short‐styled morph. Reciprocity between morphs for average stigma and anther height falls within the range of reciprocity found in other distylous Rubiaceae. Thus G. scabra is morphologically distylous but unusual among distylous species in the variation within morphs and overlap between morphs in stigma and anther heights.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Inga densiflora and I. punctata have foliar nectaries that are visited by a variety of ants. Extrafloral nectar secretion on new leaves is continuous throughout the day and night; ant activity on both old and new leaves is also continuous. Experiments compared the effectiveness of five species of ants in removing caterpillars and three other types of insect herbivores from leaves. All ant species tested could remove insect herbivores to some extent; of these ants, Pheidole biconstricta was the most effective.Leaves from which ants were excluded suffered substantially greater damage than control leaves. Ant-defense is a generalized and effective defense operating in the protection of Inga saplings against herbivores, but the extent of protection may vary according to what species of ants visit the nectariesa consequence of facultative mutualism.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Inga densiflora and Inga punctata have foliar nectaries that promote protection against herbivores by ants. Nectar-drinking ants were found to be less active at higher elevations than at lower elevations in Costa Rica, and ant defense less effective in upland populations of these trees. Herbivore damage to leaves was greater at higher elevations than at low elevation, although the abundance of lepidopteran larvae was not different. This study tested the hypothesis that lack of ant defense in Inga at high elevations is compensated for by alternative defenses. Upland I. densiflora and I. punctata had higher concentrations of phenolics in their leaves than their lowland counterparts. Extrafloral nectaries were found to be present and actively secreting nectar on plants at high as well as at low elevations. Adult wasp and fly parasitoid presence at nectar sources was greater at high elevations in the absence of ants, and parasitization of caterpillars reared from upland Inga was significantly higher than in those reared from lowland Inga. Thus, upland caterpillars on Inga are more vulnerable than those at low elevations to predators and parasitoids attracted to nectar, because at high elevations less of the nectar is taken by ants. The antiherbivore properties of upland Inga represent a novel complex of facultative defenses in the absence of protection by ants.

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