Question

why root pressure is absent in gymnosperms.

Answer 1

Root pressure is the hydrostatic pressure involved in the water movement up the xylem in the root. It results in the absorption and movement of water upto small height only and thus is observed in small herbaceous plants only. It is absent in gymnosperms as they are mostly tall plants and root pressure is not efficient mechanism to transport water upto to great heights in these plants. These plant transport water mainly by the transpirational pull mechanism.

Also root pressure is developed when all tracheary elements of xyelm i.e tracheids and vessels are present. Since in most gymnosperms vessels are absent in xylem, so root pressure is also absent.