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Featured Article: Cantus firmus

Dufay – mass cantus firmus, derived from "Se la face ay pale"

In music, a cantus firmus ("fixed song") is a pre-existing melody forming the basis of a polyphonic composition, often set apart by being played in long notes.

Popular Article: Phototropism

The light from the lamp (1.) functions as a detectable change in the plant's environment. As a result, the plant exhibits a reaction of phototropism--directional growth (2.) toward the light stimulus.

Phototropism is the growth or movement of a sessile organism or a component part of the organism toward or away from a light source. Growth or movement towards a light source is a positive phototropism, while growth away from a light source is called negative phototropism. Positive phototropism is common among the shoots of higher plants, while roots usually exhibit negative phototropism.

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Barbershop music is a four-part a cappella style of singing famous for its "ringing" chords in which an overtone is produced that sounds like a fifth note (source: Barbershop music)

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