inner epidermis, the cells also enlarge radially with plate like thickening of the walls. The mature inner integument has a palisade layer, a pigmented zone with 15–20 layers, while the innermost layer is known as the fringe layer. (Kozlowski 1972) Gymnosperms In gymnosperms, which do not form ovaries, the ovules and hence the seeds are exposed. This is the basis for their nomenclature – naked seeded plants. Two sperm cells transferred from the pollen do not develop the seed by double fertilization, but one sperm nucleus unites with the egg nucleus and the other sperm is not used. Sometimes each sperm fertilizes an egg cell and one zygote is then aborted or absorbed during early development. The seed is composed of the embryo (the result of fertilization) and tissue from the mother plant, which also form a cone around the seed in coniferous plants such as pine and spruce. Shape and appearance A large number of terms are used to describe seed shapes, many of which are largely self-explanatory such as Bean-shaped () – resembling a kidney, with lobed ends on either side of the hilum, Square or Oblong – angular with all sides more or less equal or longer than wide, Triangular – three sided, broadest below middle, Elliptic or Ovate or Obovate – rounded at both ends, or egg shaped (ovate or obovate, broader at one end), being rounded but either symmetrical about the middle or broader below the middle or broader above the middle. Other less obvious terms include discoid (resembling a disc or plate, having both thickness and parallel faces and with a rounded margin), ellipsoid, globose (spherical), or subglobose (Inflated, but less than spherical), lenticular, ovoid and sectoroid. Striate seeds are striped with parallel, longitudinal lines or ridges. The commonest colours are brown and black, other colours are infrequent. The surface varies from highly polished to considerably roughened. The surface may have a variety of appendages (see Seed coat), and be described by terms such as papillate or digitiform (finger-like). A seed coat with the consistency of cork is referred to as suberose. Other terms include crustaceous (hard, thin or brittle). Structure A typical seed includes two basic parts: an embryo; a seed coat. In addition, the endosperm forms a supply of nutrients for the embryo in most monocotyledons and the endospermic dicotyledons. Seed types Seeds have been considered to occur in many structurally different