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Galls are unique growths on plants, and how the plant's genetic instructions could produce these structures in response to external factors is still a fresh field of science. Genetic mechanisms of gall formation is a unique interplay between the parasite and the host plant in shaping the developmental trajectory of the gall organ.
The hatching larvae nourish themselves with the nutritive tissue of the galls, in which they are otherwise well-protected from external environmental effects. The host plants, and the size and shape of the galls are specific to the majority of gall wasps, with about 70% of the known species parasitizing various types of oak, inducing oak galls ...
Andricus quercuscalifornicus can induce and inhabit the galls of a variety of oak species, but they are primarily found in the galls of the Valley Oak. Due to this, they are usually found in areas such as riparian forests, open foothill woodlands, valley savannas, plant groves, and suburban areas. The wasps typically induce galls on the twigs ...
The galls occur more commonly on plants under stress, i.e. very dry conditions, waterlogging or hedge cutting, whereas vigorously growing plants are less commonly found to have galls. Whether the vigorous plant suppresses gall formation or is avoided by the wasp in favor of easier targets is unknown. Young and damaged plants tend to produce ...
Cola-nut gall cut open to show the unilocular cavity Oak marble galls showing two stunted and two normal-sized examples. The galls are found in small groups, which however do not coalesce, helping to prevent mis-identification with the oak marble gall (Andricus kollari), in addition the shape is ovoid rather than spherical and it is scaly rather than smooth.
Plant Galls in Colour. Poole: Blandford Press. ISBN 0-7137-0748-8. Hancy, Rex (2000). The Study of Plant Galls in Norfolk. Norfolk & Norwich Naturalists' Society. Redfern, Margaret & Shirley, Peter (2011). British Plant Galls. Identification of Galls on Plants and Fungi. Shrewsbury: FSC Publications. ISBN 978 1 85153 284 1.
Galls (upper left and right) formed on acorns on the branch of a pedunculate (or English) oak tree by the parthenogenetic generation Andricus quercuscalicis.. The large 2 cm gall growth appears as a mass of green to yellowish-green, ridged, and at first sticky plant tissue on the bud of the oak, that breaks out as the gall between the cup and the acorn.
P. macrosporus galls on a petiole and mid-rib of A. podagraria The gall develops as a chemically induced swelling, arising from the surface of the leaf lamina, veins, mid-ribs, and petiole. On the leaf lamina it forms yellowish bulges standing out on the upper surface, but missing the black sori that are typical of an otherwise similar gall ...