Seed are sometimes sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. Different groups of plants have other modifications, the so-called stone fruits (such as the peach) have a hardened fruit layer (the endocarp) fused to and surrounding the actual seed. Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed, such as an acorn or hazelnut. Seeds are produced in several related groups of plants, and their manner of production distinguishes the angiosperms ("enclosed seeds") from the gymnosperms ("naked seeds"). Angiosperm seeds are produced in
Stars named after people program, it was common for astronauts to be trained in celestial navigation, and to use a list of naked-eye stars which to take bearings. As a practical joke, Gus Grissom gave names to three stars on this list, which were references to the three Apollo 1 crew: The names stuck, perhaps "in memoriam" for their deaths in the Apollo 1 fire, and were used through the rest of the program. Unknown to Grissom, these stars already had traditional names; however, those were not generally used, allowing the three new names to make their way into other records. Today, they are