वन उत्पादन एवं काष्ठ उपयोग

In angiosperm wood (hardwoods):
Vessels (pores) are the specialized, open-ended tube-like conductive cellular elements primarily responsible for the vertical conduction of sap (water and dissolved mineral salts).
In gymnosperm wood (softwoods), vessels are absent, and conduction is performed by tracheids.
Medullary rays function in radial conduction and storage, while tyloses are balloon-like outgrowths that block old vessels.

Detailed analysis of options:

• Tylosis: Ingrowth of adjacent ray or axial parenchyma cells through pit cavities into the lumina of xylem vessels (pores) during heartwood formation, blocking fluid conduction.
• Ring porous woods: A pattern where large earlywood pores form a distinct concentric ring.
• Tracheids: Elongated, tapering xylem conducting and supporting cells.
• Fibres: Thick-walled mechanical supporting cells in angiosperm wood.

Characteristics of good vs. bad fuelwoods:
Lyonia ovalifolia (commonly known as Ayar, family Ericaceae, found in the temperate Himalayas) is classified as a bad fuelwood because its wood and leaves contain toxic andromedotoxins (grayanotoxins) that emit noxious, acrid, eye-irritating, and poisonous smoke when burned, making it dangerous for indoor cooking and heating.
In contrast, Casuarina equisetifolia is the world's best fuelwood ('best firewood of the world'), and Grewia optiva burns cleanly with high calorific value.