The crystal habit of a mineral describes its visible external shape. It can apply to an individual crystal or an assembly of crystals. In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. Each crystal can be described by how well it is formed, ranging from euhedral, to subhedral, and anhedral. The many terms used by mineralogists to describe crystal habits are useful in communicating what specimens of a particular mineral often look like. Recognizing numerous habits helps a mineralogist to identify a large number of minerals. Some habits are distinctive of certain minerals, although most minerals exhibit many differing habits. Crystal habit may mislead the inexperienced as a mineral's internal crystal system can be hidden or disguised.
Monday, 4 June 2012
The Yellowroot (Xanthorhiza simplicissima, syn. X. apiifolia) is the only member of the genus Xanthorhiza, and one of very few genera in the family Ranunculaceae with a woody stem (the other notable example being Clematis). It is native to the eastern United States from Maine south to northern Florida and west to Ohio and eastern Texas.
The genus name as well as the common name refer to the plant's yellow roots (xantho- meaning "yellow" and rhiza meaning "root"), which was used to produce a yellow dye by Native Americans. The species name refers to the simple (not branched) root.
Closeup of yellowroot's flowers
In the wild, it grows on the edges of streams in sandy soil under a canopy of dappled sunlight. In cultivation, it is often provided with more sunlight so that the fall colors are more vivid. It is a subshrub, reaching 20-70 cm (rarely 90 cm) in height, with stems up to 6 mm diameter. The leaves are spirally arranged, 10-18 cm long, each divided into 5 toothed leaflets, and flowers emerge only from the upper portion of the unbranched stem. The flowers are produced in broad panicles 6-20 cm long, each flower small, star-shaped, reddish brown to purple brown, with five petals.
Yellowroot propagates asexually by sending out many underground runners, and it reproduces sexually with seeds.
Yellowroot is comparatively rare in British gardens, although E.H. Wilson and E.A. Bowles are among distinguished plantsmen to have championed its merits. It was grown by Bowles in his garden at Myddelton House, near Enfield, Middlesex, and gardens that currently cultivate it include the Savill Garden at Windsor, Berkshire and the Westonbirt Arboretum near Tetbury, Gloucestershire. Wilson, who regarded yellowroot as one of the best plants for hardy deciduous ground cover, also described (in 1923) its use in the Arnold Arboretum at Harvard University in Massachusetts.
Tuesday, 20 September 2011
Habits (or wonts) are routines of behavior that are repeated regularly and tend to occur subconsciously. Habitual behavior often goes unnoticed in persons exhibiting it, because a person does not need to engage in self-analysis when undertaking routine tasks. Habituation is an extremely simple form of learning, in which an organism, after a period of exposure to a stimulus, stops responding to that stimulus in varied manners. Habits are sometimes compulsory.