- In biology, a substrate is the surface on which an organism (such as a plant, fungus, or animal) lives. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock (its substrate) can be itself a substrate for an animal that lives on top of the algae. Inert substrates are used as growing support materials in the hydroponic cultivation of plants. In biology substrates are often activated by the nanoscopic process of substrate presentation.
- Four corners of the world (Wikipedia)
Several cosmological and mythological systems portray four corners of the world or four quarters of the world corresponding approximately to the four points of the compass (or the two solstices and two equinoxes). At the center may lie a sacred mountain, garden, world tree, or other beginning-point of creation. Often four rivers run to the four corners of the world, and water or irrigate the four quadrants of Earth.