Crossing(redirected from Crossings)
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a ventilation device installed in underground mine workings and designed to separate and isolate intersecting flows of air, such as fresh air and exhaust air. Depending on the airflow and period of service, crossings may be made of metal and concrete piping or in the form of a well-secured bypass shaft driven through the rock in the roof or soil of the bed.
(also interbreeding or hybridizing), one of the methods of the selective breeding of plants and animals. Crossing is used to obtain hybrids and crossbreeds that represent the initial material in selection and culling for economically beneficial characteristics. It is also used in the development of new breeds and varieties.
The various systems of crossing can be classified in one of two categories: inbreeding and outbreeding. Variants of outbreeding include crossbreeding, incrossing (crossing inbred lines of the same breed or variety), incrossbreeding (crossing inbred lines of different breeds or varieties), topcross (crossing specially selected inbred male lines with outbred female lines), and more remote crossings. In animal breeding, crossing is understood to mean crossbreeding, which is divided into induced crossbreeding, reproductive crossing, grading up, and commercial crossbreeding. (See alsoHYBRIDIZATION.)
in medieval, primarily Romanesque and Gothic, churches, the place where the nave and transept intersect.