A large tree adds a new growth ring of xylem cells for conducting water every year. The so-called diuse-porous woods, such as maples and magnolias, develop many xylem vessels of intermediate radius, or 45 m. On the other hand, oaks, elms, and other ring-porous woods develop fewer xylem vessels of greater radius, or 90 m. Let us assume that all features of the conducting vessels are identical in these trees, except for the dierent radii of their vessels.
(a) In a new growth ring, a maple tree can develop 10,000 new vessels with a radius of 45 m. How many vessels of radius 90 m would have to develop in a new growth ring of an oak tree to have an equal rate of total xylem ow as in the maple? Show your calculations using equation (2).
(b) Clearly, it is advantageous to have such large vessels for the purpose of maximal water conduction, but can you think of a plausible reason why the tallest and longest-living trees have many narrow water-conducting cells rather than fewer wide ones?