Almost any vascular plant can be measured in the pressure chamber. Twigs, branches, herbs, grasses, and fruits of a variety of species have been measured successfully.
Twigs and branches
Most of the early work with the pressure chamber was done with woody plants because they are easiest to measure. Secondary lateral twigs of large trees can be used, but the entire top of seedlings may be required. In woody species the phloem (bark) should be stripped back from the cut surface about 2 cm (about 3/4″) to allow the xylem (woody portion) to protrude through the gasket.
Selecting a proper sized Compression Gland Gasket and Compression Gland Insert is important. Ensuring that you use the proper Compression Gland Gasket and Compression Gland Insert with the proper Compression Gland Base is important not only for sealing properly but for safety also.
Herbaceous plants are only slightly more difficult to measure than woody plants. Sealing the sample in the gasket without crushing or kinking the stem is usually the biggest problem. This can sometimes require creative methods of measurement.
The endpoint may be difficult to determine, but a good lighting or a lighted magnifier will be helpful. The use of a microscope to aid them in seeing the endpoint is sometimes used in very small samples but such measures are usually not necessary.
With herbs it is especially important to measure the sample immediately after cutting and to use the proper rate of pressure increase.
Measuring grass can be more difficult than round or semi-round samples. While it is sometimes possible to measure the round portion of the stem it is normally more successful using the flat portion of a leaf blade. The Grass Compression Gland Sealing System is normally the best way to seal the blade into the chamber.
Measuring fruits such as apples, oranges, or tomatoes is not difficult, but the fruit must usually be supported in the chamber. A coil spring in the bottom of the chamber is helpful. Once the sample is in the chamber measurements can proceed as with herbs.