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Caruncle and Aril: Structures and Significance
| Feature | Caruncle | Aril |
|---|---|---|
| Definition | A spongy, bilobed outgrowth of the outer integument or testa of the seed. Found in castor seed (Ricinus communis), soft and fleshy. | A post-fertilization fleshy, collar-like outgrowth of the funicle at the micropylar end in the pericarp. |
| Functions |
|
|
| Fleshy Aril in Litchi | Not present. | The edible part of litchi (Litchi chinensis) is the fleshy aril, surrounding the seed. It is sweet, juicy, and rich in sugars. |
| Fleshy Aril in Nutmeg | Not present. | In nutmeg (Myristica fragrans), the aril is called mace (जायपत्री / जावित्री in Hindi). It is a bright red, lacy covering around the nutmeg seed, used as a spice. |
| Aril in Pomegranate | Not present. | In pomegranate (Punica granatum), the juicy red arils surround each seed, aiding in seed dispersal by attracting animals and birds. |
Detailed Explanation of Seed and Fruit Structures with Deep Reasoning
| Diagram / Section | Label / Component | Detailed Explanation | Function / Significance |
|---|---|---|---|
| Dicot Seed | Seed Coat (Testa) | The outer protective layer derived from the integuments of the ovule. It may be hard or leathery and is often pigmented. | Shields the embryo from mechanical damage, pathogens, and controls water uptake during germination. |
| Dicot Seed | Cotyledons | Seed leaves that are often large and store vital nutrients such as starch, proteins, and lipids. They may later become photosynthetic. | Supply essential nutrients to the young seedling until it can produce its own food through photosynthesis. |
| Dicot Seed | Embryo (Plumule & Radicle) | The miniature plant within the seed, with a plumule (future shoot) and radicle (future root). In many diagrams, the embryo is centrally located. | Initiates the growth of the new plant once favorable conditions occur. |
| Dicot Seed | Micropyle | A small opening in the seed coat formed during ovule development. It is the site where the pollen tube entered and later serves as an entry point for water. | Facilitates water absorption (imbibition) that triggers germination. |
| Dicot Seed | Hilum | A scar on the seed surface marking the point of attachment to the ovary via the funicle. It often appears as a distinct spot. | While not directly involved in growth, it serves as an identification mark and indicates the seed’s origin. |
| Dicot Seed | Endosperm (when present) | A nutritive tissue that sometimes surrounds the embryo. In many dicots, it is absorbed by the cotyledons during development. | Provides essential nutrients during early stages of seed germination. |
| Monocot Seed (Maize) | Seed Coat (Testa) | The protective outer layer of the seed, often pigmented and derived from the ovule’s integuments. | Protects the seed from external damage and regulates water absorption. |
| Monocot Seed (Maize) | Endosperm | A large, persistent tissue that stores nutrients such as starch, proteins, and lipids. It remains intact even during germination. | Acts as the primary energy reserve, supplying nutrients to the developing embryo. |
| Monocot Seed (Maize) | Scutellum | A modified cotyledon unique to monocots that is adapted for absorbing nutrients from the endosperm. | Facilitates the transfer of nutrients from the endosperm to the embryo during germination. |
| Monocot Seed (Maize) | Coleoptile | A protective, pointed sheath that covers the emerging shoot. It is visible as the first structure to break through the soil. | Guards the delicate shoot from physical damage and abrasion as it grows upward. |
| Monocot Seed (Maize) | Coleorhiza | A sheath covering the emerging radicle (embryonic root), similar in function to the coleoptile but for the root system. | Protects the tip of the emerging root during the early stages of growth. |
| Monocot Seed (Maize) | Embryo | The developing plant that includes the shoot and root primordia, encased by the protective layers. | Contains all the genetic and structural material necessary for the plant to grow after germination. |
| Apple (Pome/False Fruit) | Hypanthium (Thalamus) | A fusion of floral parts (such as the bases of sepals, petals, and stamens) that forms the bulk of the edible tissue. It is derived from the floral receptacle rather than solely the ovary. | Provides the fleshy, attractive part of the fruit that entices animals for seed dispersal. |
| Apple (Pome/False Fruit) | Ovary (Carpellary Core) | The structure that encloses the ovules. In apples, the ovary is modified and forms the central core where the seeds are located. | Houses the seeds and contributes structurally to the fruit’s formation. |
| Apple (Pome/False Fruit) | Endocarp | The innermost layer of the ovary wall, which in apples may harden to form a protective barrier around the seeds. | Protects the seeds from physical damage and supports seed viability. |
| Apple (Pome/False Fruit) | Mesocarp | The middle layer of the ovary wall that develops into the fleshy, edible portion of the fruit. It accumulates sugars and nutrients. | Provides a nutrient-rich, appealing tissue that attracts animals for dispersal. |
| Apple (Pome/False Fruit) | Exocarp | The outer skin of the fruit, often containing waxes and pigments that add color and protection. | Acts as a barrier against pathogens and environmental stress while reducing water loss. |
| Strawberry (False Fruit) | Receptacle (Thalamus) | An enlarged, fleshy structure derived from the flower’s receptacle rather than the ovary. It forms the bulk of what we consider the “fruit.” | Provides the sweet, edible tissue that attracts animals, aiding in seed dispersal. |
| Strawberry (False Fruit) | Achenes | Small, dry, one-seeded fruits that are embedded on the surface of the receptacle. Each achene is the true fruit containing a single seed. | Ensures the propagation of the strawberry plant by housing the actual seeds, which are then spread by animals. |