Question

Differentiate between:
A. Hypocotyl and Epicotyl
B. Coleoptile and Coleorhiza
C. Integument and Testa
D. Perisperm and Pericarp

Answer 1

Hint: The position and function of these structures in a plant are sufficient to differentiate between them. Moreover, all of these are related to the seeds and ovules of a plant. The seed consists of various parts and layers. The above-given terms define those parts of layers.

Complete answer:
a) Hypocotyls and Epicotyl: The hypocotyl is that part of the embryonic axis that lies in between the cotyledonary node and the radical. It forms an essential part of the embryonic root system. As it is present above the radical and just below the cotyledons, it is called the stem of the germinating seed. It is the primary organ of a young plant that develops into a stem and thus helps it to extend. The hypocotyl is terminated with the radical. On the other hand, epicotyl is that part of the embryonic axis that is situated between cotyledons and the plumule. It plays an important role in the initial stages of plant life. It forms the essential portion of the embryonic shoot system. It grows rapidly to extend the stem above the ground level. The epicotyl is terminated along with the plumule.
b) Coleoptile and Coleorhiza: Coleoptile is a protective sheath that surrounds the tip of the shoot in monocot seeds. It grows up with the plumule up to a certain point. It consists of two vascular bundles on each side. It lacks chlorophyll so it is pale in colour. Some of the coleoptiles have purple colour due to the presence of anthocyanin. Coleorhiza is also a sheath present in monocot seeds. It surrounds the radical and connects to the primary root. It does not grow to considerable length. It stops growing once it emerges out of the seed and the rest remains in the soil.
c) Integument and Testa: The integument is the outermost protective covering of the ovule. In angiosperms, there are two integuments and in gymnosperm, there is only one integument. It consists of smooth and thin living cells. It develops into a testa once fertilization takes place. Hence, it is a pre-fertilization structure. Testa on the other hand is an exterior protective covering of the seed. It is brown in appearance as it emerges from outer integuments. It is a post-fertilization structure. It protects the seed when the seed stays in dispersed conditions. It also helps in seed dormancy as it is impermeable to water.
d) Perisperm and Pericarp: Perisperm is the persistent remains of nucellus in the ovule inside the seed. It is dry in texture. But Pericarp is the wall of fruit formed by the ovarian wall. It can be fleshy or dry.

Note: The grains of grasses are single-seed simple fruits wherein the pericarp (ovary wall) and seed coat are fused into one layer. This type of fruit is called a caryopsis. Examples include cereal grains, such as wheat, barley, and rice.