Q.Why do internodal segments of sugarcane fail to propagate vegetatively even with they are in contact with damp soil.

Dioscorea reproduces vegetatively via axillary bulbils; the other listed plants use different vegetative organs.

Bulbils are fleshy, modified vegetative or floral buds that develop, store food, detach from the parent plant, and germinate into new individuals — a form of natural vegetative propagation. Dioscorea (yam) is the classic example, producing bulbils in the axils of its leaves; when they fall off, each bulbil is capable of growing into a complete new plant.

…

Onion multiplies vegetatively using a bulb, a modified underground stem.

Vegetative propagation allows a new plant to arise from a vegetative part (root, stem, or leaf) of the parent without seed formation. In onion (Allium cepa), the underground stem is modified into a bulb — a short, disc-like stem covered by fleshy scale leaves that store food. Under favourable conditions, axillary buds within the bulb sprout to give rise to new plants (and dau …

Sugarcane can only propagate vegetatively from its nodal buds, so an internodal cutting without any node simply cannot sprout a new plant, however damp the soil.

Vegetative propagation in sugarcane occurs through stem cuttings, but specifically requires the presence of a node, which bears the dormant axillary bud ('eye') that is capable of sprouting into a new shoot, along with adventitious roots. The internodal region of the stem, lying between two nodes, has no such bud tissue capable of regenerating a whole new plant. Therefore, even if internodal cuttings of sugarcane are kept in continuous contact with damp/moist soil (ideal conditions for rooting), they cannot vegetatively propagate, be …

Grafting requires a vascular cambium to knit the graft union; monocot vascular bundles are closed (cambium-less), so grafting is not possible.

Grafting is a method of vegetative/asexual propagation in which a piece of one plant (the scion) is joined to the rooted stem of another (the stock), and the two grow together as a single plant because the cambium of each forms callus tissue that unites the vascular systems across the graft junction — a process that depends on the presence of a functional (secondary) vascular cambium capable of producing new xylem and phloem.

…

Bryophyllum reproduces vegetatively through leaves; the other options propagate by different vegetative organs.

Vegetative propagation is a form of asexual reproduction in which a new plant develops from a vegetative part (root, stem or leaf) of the parent plant, without the fusion of gametes. Bryophyllum (also called Kalanchoe) is the classic textbook example of propagation by leaves: the notches along the leaf margin contain groups of meristematic cells (adventitious buds) that, given moist conditions, develop roots and shoots even while still attached to the leaf. When the leaf falls to the ground, each of these plantlets separates and grow …