Which of the following characters represent the affinities of Gnetum w...
Characteristics of Gnetum
Gnetum is a genus of gymnosperms that includes around 40 species of woody vines and trees. The characteristics of Gnetum are as follows:
- Presence of xylem vessels: Gnetum has xylem vessels, which are tubular structures that transport water and minerals from the roots to the leaves. This is a characteristic shared with angiosperms, which are flowering plants that also have xylem vessels.
- Absence of archegonia: Gnetum does not have archegonia, which are structures that produce eggs and are found in some other gymnosperms, such as Cycas and Pinus.
- Differences with Cycas and Pinus: Cycas and Pinus are two other genera of gymnosperms that are different from Gnetum in several ways, including:
- Cycas has a perianth, which is a whorl of petal-like structures that surround the reproductive organs. Pinus does not have a perianth, and Gnetum does not have a perianth either.
- Pinus has two integuments, which are layers that surround the ovule and develop into the seed coat. Cycas and Gnetum have only one integument.
- Cycas and Pinus have a different kind of embryo development than Gnetum. In Cycas and Pinus, the embryo develops within the ovule, while in Gnetum, the embryo develops outside the ovule.
- Cycas and Pinus have a visible apical meristem, which is a region of actively dividing cells at the tip of the stem. Gnetum also has an apical meristem, but it is not as visible as in Cycas and Pinus.
- Conclusion: Therefore, the correct answer is option 'A', which states that the presence of xylem vessels and absence of archegonia are the characteristics that represent the affinities of Gnetum with angiosperms and differences with Cycas and Pinus.
Which of the following characters represent the affinities of Gnetum w...
Bnetum resembles with the gymnosperms on one hand and theangiosperms on the other.
Resemblace with the gymnosperms:
(i)Ovary is absent and ovules are naked
(ii) Style and stigma are absent.
(iii) Pollination is anemophilous.
(iv) Fruits are not formed
Resemblace with the angiosperms:
(i) In general habit it is climber as tree-like.
(ii) Leaves are broad, green and with reticulate venation.
(iii) Archegonia are latogether absent in the female gametophyte.
(iv) Absence of free nuclear divisions in the embryo sac.
(v) Endosperm completes its development after the fertilization.
(vi) Xylem vessels are present.
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