Practice question

Early vascular plants relied almost exclusively on tracheids as principal xylem conduits, reflecting ancestral condition retained in most ferns, lycophytes and gymnosperms. These elongated, tapered, dead cells at maturity possess lignified walls with annular, helical and bordered pits allowing lateral water movement between adjacent tracheids and structural support. Vessel elements evolved later predominantly in angiosperms and some gnetophytes offering more efficient conduction through perforation plates. Sieve cells and companion cells belong to phloem transport system, not xylem water conduction. This structural framework illustrates phylogenetic relationships and adaptive significance highlighted in competitive examinations focusing on comparative plant morphology and systematics.