Tag: seeds - structure and germination

In hypogeal germination, the cotyledons do not come out of the soil surface. In such seeds, the epicotyl (i.e., part of the embryonic axis between plumule and cotyledons) elongates pushing the plumule out of the soil. All monocotyledons show hypogeal germination.

Maize is a member of the Poaceae family, which are monocotyledonous plants, whereas beans, peas, and gram are dicotyledonous.

Epigeal germination is characterized by the hypocotyl elongating and pushing the cotyledons above the soil surface.

Pea and castor are dicots (2 cotyledons), while maize is a monocot (1 cotyledon). Thus, the sequence is 2, 2, and 1.

In monocot seeds, the coleorhiza protects the radicle, and the coleoptile protects the plumule during germination.

Dicotylodoneae is a group of angiosperms that are characterized by tap root system, vascular tissue present in columns, posses xylem vessels, leaves have reticulate venation, stem with open collateral vascular bundles arranged in a ring and seed are covered by fruits and show secondary growth.

Perisperm differs from endosperm in being a diploid tissue. Endosperm is a tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. These are typically triploid but can vary widely from diploid. Endosperm that is diploid, resulting from the fusion of a pollen nucleus with one, rather than two, maternal nuclei.They are both nutritive layers in a seed. Perisperm develops from the nucellus of the seed and the endosperm develops when the sperm cell fuses with two haploid polar nuclei (contained in the central cell) in the centre of the embryo sac (or ovule). The resulting cell is triploid (3n). This triploid cell divides through mitosis and forms the endosperm, a nutrient-rich tissue, inside the seed. 

Composite fruit is a type of fruit that develops from an inflorescence rather than from a single flower while custard apple fruit develops from a polycarpellary and apocarpous ovary. It forms from the pistils and receptacle of one flower. Custard apple is an example of aggregate fruit.

The coconut is also a drupe, but the mesocarp is fibrous or dry (termed a husk), so this type of fruit is classified as a simple dry fruit, fibrous drupe. Unlike other drupes, the coconut seed is unlikely to be dispersed by being swallowed by fauna, due to its large size. It can, however, float extremely long distances across oceans.