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Fig. 7.1-6. Transverse section of pine wood (Pinus). All cells in this micrograph are tracheids. You can not tell that from simply looking at this section, but rather by knowing that it is a sample of pine, which has lacks both vessels and fibers. The three arrows indicate circular bordered pits; any cell with bordered pits will be a tracheary element, not a fiber. If this were an unknown sample, you could search for perforations -- if these were vessels, a perforation should be visible somewhere (although in transverse section, it might be difficult to recognize). An important clue that these are tracheids and not vessels is that they are all so similar in diameter -- they are uniformly large in the earlywood and uniformly smaller in the latewood. Vessels typically are present in several sizes, and are virtually always associated with other cells that are smaller than they. The uniformity here, along with the circular bordered pits, indicates that these are tracheids.

            Could this be a mix of tracheids and fibers? After all, many of the cells do not have circular bordered pits in this view. To be certain that there are no fibers present, it would be necessary to examine many transverse sections and check to make certain some cells completely lack circular bordered pits. Or longitudinal sections could be checked -- that is much easier and faster. But keep in mind that conifers like pines are called softwoods because they lack xylary fibers.