Main Difference

The main difference between Hypocotyl and Epicotyl is that Hypocotyl is the region below the seed leaves (cotyledon), whereas Epicotyl is the region above the cotyledon of the stalk.

Hypocotyl vs. Epicotyl

Hypocotyl plays a role in epigeal germination in such a way to ensure the cotyledons come out of the soil, whereas epicotyl has a role in the hypogeal germination, which is responsible for keeping the cotyledons inside the soil. Hypocotyl lies between the node of cotyledon and radicle (embryo root), while epicotyl lies between the plumule (first shoot that grows from the part of seed embryo) and node of the cotyledon. Plumule is the terminal end of the epicotyl, whereas the radicle is the terminal end of the hypocotyl.

Hypocotyl develops into a structure of stem from which root develops, while the epicotyl develops into the structure of stem, which bears leaves, fruit, and flowers. The growth of the hypocotyl initiates from the radicle, while the growth of the epicotyl starts from the node of the cotyledon.

Hypocotyl serves as the main elongation structure, which develops into the first part of the stem, which bears the flower, fruit, and leaves. Epicotyl serves to elongate the embryonic shoot from which true roots develop.

Cotyledons of the hypocotyl are green, so exhibit the photosynthetic activity; on the other hand, cotyledons of epicotyl are not photosynthetic. Hypocotyl has cotyledons out of the soil. Epicotyl has cotyledon inside of the soil.

Comparison Chart

What is Hypocotyl?

Hypocotyl is the region that extends out through the epigeal germination (in which hook-like structure also formed) into a first part of the stem from which root develops. Hypocotyl serves as the region in between the node of the cotyledon (Cotyledons can be monocotyledon and dicotyledonous) and radicle (a part of root embryo). Radicle is the terminal end of the hypocotyl at which it ends its growth. Hypocotyl elongation is also affected by the auxin (phytohormone) induces the rapid elongation of the hypocotyl. In monocot plants, the hypocotyl is not above the ground because stem elongation is not the characteristic of the monocot.

The portion of the hypocotyl lies below the green cotyledons, so they are photosynthetic in nature. The growth of the hypocotyl is controlled by the photomorphogenesis (development of the plant’s structure affected by light other than photosynthetic light). The seedlings in the shade may lead to the transcriptional response, which negatively causes to increase the rate of hypocotyl growth. If plants are exposed to darkness, then the process occurs called skotomorphogenesis in contrast to photomorphogenesis.

In some plant species, hypocotyl may become enlarged, called storage organ as well in some species it can grow above the ground. Examples of hypocotyl are Gloxinia, and Cyclamen (it’s storage organ called tuber), Celeriac.

Hypocotyl germinates through the epigeal germination, which helps the cotyledons to come out of the soil. The cotyledons of the epigeal germination is out of the ground. Examples include bean, castor, cotton, papaya, onion, etc.

What is Epicotyl?

Epicotyl is the region that lies above the cotyledon of the embryo in angiosperms. Epicotyl is present between the node of cotyledon and plumule. Epicotyl is covered by coleoptile (protective sheath). The terminal point of the epicotyl is the plumule. Epicotyl serves to germinate inside the soil below the ground. Epicotyl develops into the part of the stem, which lies above the ground from which leaves, fruit, and flowers. Epicotyl’s lengthening is controlled by the phytochrome photoreceptors (class of photoreceptors, which are sensitive to red and far-red regions of the light. Cotyledons of the epicotyl do not exhibit the photosynthetic activity.

In the dicot seeds, epicotyl is hook-like in shape, having plumule in the downward direction. Plumule hook when it comes out of the abrasive soil, it is then damage protected.

Epicotyl germinates through the hypogeal germination, which ensures the cotyledons to stay below the soil. The cotyledons of the hypogeal germination are below the ground. Examples are as Pea, Runner bean, Eutacta, Mango, Maize, Rice.

Key Differences

1. The hypocotyl part of the germinating seedling lies above the ground, whereas the epicotyl part lies below the ground.
2. Hypocotyl lies below the seed leaves of the embryo; on the flip side, epicotyl lies above the cotyledons of the embryo.
3. The hypocotyl is between the plumule and node of cotyledon; on the other hand, epicotyl is between the plumule and node of the cotyledon.
4. The hypocotyl germinates through the epigeal germination (role in the development of plant below the ground), while epicotyl germinates through the hypogeal germination (role in the development of plant above the ground).
5. The termination point of the hypocotyl is the cotyledonary node; conversely, the termination point of the epicotyl is from the plumule.
6. The hypocotyl develops into the structure from which development of root occurs, whereas epicotyl develops into the upper parts of the stem with the flowers, fruits, and leaves.
7. In epigeal germination, hypocotyl extends to bring the cotyledons out; on the flip side, in hypogeal germination, epicotyl extends to keep the cotyledons inside the soil.
8. Cotyledons of the hypocotyl are photosynthetic as they are green, whereas cotyledons of the epicotyl are not photosynthetic.
9. The cotyledon of the embryo is out of the soil in hypocotyl; on the other hand, cotyledon of the embryo is inside the soil in epicotyl.

Conclusion

The hypocotyl germinates through the epigeal germination below the cotyledon, whereas epicotyl germinates through the hypogeal germination above the cotyledon.