Definition of PLACOID. : of, relating to, or being a scale of dermal origin with an enamel-tipped spine characteristic of the elasmobranchs. ADVERTISEMENT.Greek plak-, plax flat surface.First Known Use: 1842.efinition of PLACOID. : of, relating to, or being a scale of dermal origin with an enamel-tipped spine characteristic of the elasmobranchs. ADVERTISEMENT. Greek plak-, plax flat surface. First Known Use: 1842.
A tree pruner is a class 1 lever. The fulcrum is where the two blades cross, and the load is what you are cutting. The effort is applied to the two handles.
A nut may be defined as a one-seeded fruit with a hard pericarp (ripened ovary wall). One or several nuts may sit in a cup-shaped structure called an involucre. In oaks (Quercus) the involucre is composed of small scales and the entire structure (involucre plus nut) is called an acorn.hese false nuts are really the seed-bearing, hard, inner layer (endocarp) of a fruit called a drupe. In dry drupes the outer layer or husk sometimes splits open or withers. This outer husk is part of the ovary wall (pericarp), and the hard inner wall surrounding the seed represents the inner part of the pericarp.