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
Archaeological sub-disciplines Archaeological sub-disciplines As with most academic disciplines, there are a number of archaeological sub-disciplines typically characterised by a focus on a specific method or type of material, geographical or chronological focus, or other thematic concern. Certain civilizations have attracted so much attention that their study has been specifically named. These sub-disciplines include "Assyriology" (Mesopotamia), "Classical archaeology" (Greece and Rome), "Etruscology" (Etruria), and "Egyptology" (Egypt). Another main division of archaeology distinguishes: In areas of semi-literacy the term A selective list of sub-disciplines distinguished by time-period or region of study might include: The following is a list of other sub-disciplines. Some of