Permeability of the Cambium to Air in Trees Adapted to Wet Habitats

The permeability of the cambium to gas exchange varies significantly among tree species The amount of tension required to pull air across the cambium of water tupelo and green ash is sufficiently low to permit free gas exchange with the atmosphere, whereas air movement is restricted across the cambia of sweetgum, yellow poplar, and sycamore Water tupelo and green ash stems possess prominent intercellular spaces among the cambial ray initials forming an open interconnecting aeration system between the xylem and phloem rays on either side Similar openings in the cambium are absent or less than 1 μ in size in the other species examined. In mesophytic trees the transpiration stream undoubtedly plays a vital role in supplying oxygen to, and removing carbon dioxide from, the actively dividing and differentiating cells on the xylem side of the relatively impervious cambium Conversely, in hydrophytes where air is often limiting to the roots and water is plentiful the cambium is increasingly more permeable to air.