The Density of Wood Tissue

The density of oven-dry cell tissue of all woody plants is roughly 1500 kg m. It can be accurately determined with a pycnometer, a small vessel (c. 10 ml) with a ground glass stopper having a concentric capillary bore to allow excess liquid to escape when filling the vessel. The pycnometer can be filled with a highly reproducible 

However, when water was used the pycnometric density of the cell wall was calculated to be 1545 kg m . This is some 5% greater than the previous value (Table 3.2). Two faetors are responsible for this difference  

A further experiment is needed to determine the relative importance of these effects. When a water-swollen specimen is placed in successive water-alcohol 

it is possible that a little of the more strongly adsorbed water or alcohol is not displaced during solvent exchange by the hexane which would introduce an error here and in subsequent calculations. 

The difference between the oven-dry cell wall density determined using silicone and after solvent exchange using an inert liquid like hexane must be due to the presence of residual sub-microscopic pores within the oven-dry cell wall, that are only penetrated when the cell wall is swollen. Accordingly, the inaccessible void volume per kg of cell wall material can be determined from the difference between the apparent volume of the cell wall material in silicone and the true volume as measured in the solvent-exchanged hexane. This is 0.0303 x 10 m per kg, or about 4% on a volume basis, i.e. (0.0303/0.6825) x 100% (Table 3.2). 

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