Water Vapor Diffusion through Eastern Hemlock Periderm

Marshall S. White


Physiologically, rhytidome on the living tree has been considered a moisture barrier. It is proposed in this study that the periderm tissue in eastern hemlock inhibits moisture movement and may, therefore, prevent desiccation of the living secondary phloem. The kinetics of water vapor sorption by several periderm tissues were measured and compared.

Moisture movement into and through layers of thin-walled phellem and phelloderm and thick-walled phellem and phelloderm was monitored on specilly prepared samples. Both phellem and phelloderm tissues are equally resistant to moisture flow. Transient diffusion coefficients determined for both thick-walled tissues were 30 times lower than those reported by others for wood and one tenth those for the thick-walled tissues for similar moisture contents.

Periderm tissues seem uniquely responsible for inhibited moisture flow in hemlock bark rhytidome with the thick-walled phellem and phelloderm most influential in this regard.


Bark;rhytidome;sorption;phellem;phelloderm;Tsuga canadensis

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