Axial water permeability was measured on the specimens of coast and mountain types of Douglas-fir (Pseudotsuga menziesii FRANCO) sap- and heartwood, in green and air dried conditions. The measurement was carried out on the water saturated specimens of various lengths from 0.4 to 3.2cm in the fiber direction. Conducting tracheids, which were labeled with 0.5% water solution of Rhodamine B fluorochrome through the wood specimens, were observed with a reflected light fluorescence microscope in order to make clear the path-way, and the conducting area in the cross section of specimen was also measured on the specimens of various lengths.
Most of sapwood specimens in green were quite permeable and their permeability was constant in any specimen length. However, the air dried sapwood specimens of coast type showed very low permeability 3.5×10^-2 darcy even in the specimen length of 0.4cm, which corresponds to its fiber length. The permeability K in darcy decreased exponentially with increasing specimen length l in cm, as follows.
logK=-0.19·l-1.84
R²=0.52
On the other hand, for the air dried sapwood specimens of mountain type, the one with specimen length of 0.4cm gave the same high permeability as that of green condition, and the permeability was expressed by the following equation (see Fig. 2),
logK=-0.63·l+0.52
R²=0.87
These results agree with Bramhall's consideration.
In green sapwood, water conduction occured in the whole early wood and a part of late wood. In drying, pits in early wood were blocked by aspiration and became to be impermeable. However, conducting tracheids in late wood, which has low permeability even in green, still remained under a air dried condition. Therefore, in air dried sapwood, most of the conducting tracheids were in late wood (see Fig. 5 (a)(b)).
The measured values of conducting area for the specimens of various lengths did not correspond to those calculated from the permeability according to Bramhall's equation. The reduction in conducting area e^-bl, as Bramhall said, should be understood as the reduction in number of conducting pits, because, for example, air dried sapwood of mountain type had the measured conducting area of 50% against 10% calculated from b vlue of 1.46. The former represented the total area of tracheids labeled with fluorochrome even if their permeability was very low, while the latter corresponded to the conductivity in pits between tracheids.