fruit to a tier. The hanging cluster is known as a bunch, comprising 3–20 tiers, or commercially as a "banana stem", and can weigh . Individual banana fruits (commonly known as a banana or "finger") average , of which approximately 75% is water and 25% dry matter (nutrient table, lower right). The fruit has been described as a "leathery berry". There is a protective outer layer (a peel or skin) with numerous long, thin strings (the phloem bundles), which run lengthwise between the skin and the edible inner portion. The inner part of the common yellow dessert variety can be split lengthwise into three sections that correspond to the inner portions of the three carpels by manually deforming the unopened fruit. In cultivated varieties, the seeds are diminished nearly to non-existence; their remnants are tiny black specks in the interior of the fruit. The end of the fruit opposite the stem contains a small tip distinct in texture, and often darker in color. Often misunderstood to be some type of seed or excretory vein, it is actually just the remnants from whence the banana fruit was a banana flower. Banana equivalent radiation dose As with all living things on earth, potassium-containing bananas emit radioactivity at low levels occurring naturally from potassium-40 (40K or K-40), which is one of several isotopes of potassium. The banana equivalent dose of radiation was developed in 1995 as a simple teaching-tool to educate the public about the natural, small amount of K-40 radiation occurring in every human and in common foods. The K-40 in a banana emits about 15 becquerels or 0.1 microsieverts (units of radioactivity exposure), an amount that does not add to the total body radiation dose when a banana is consumed. By comparison, the normal radiation exposure of an average person over one day is 10 microsieverts, a commercial flight across the United States exposes a person to 40 microsieverts, and the total yearly radiation exposure from the K-40 sources in a person's body is about 390 microsieverts. Etymology The word "banana" is thought to be of West African origin, possibly from the Wolof word , and passed into English via Spanish or Portuguese. Taxonomy The genus Musa was created by Carl Linnaeus in 1753. The name may be derived from Antonius Musa, physician to the Emperor Augustus, or Linnaeus may have adapted the Arabic word for banana, mauz. According to Roger