Fig. 8.1-4b. Transverse section of parsnip (Pastinaca) stem. The sieve tube members (several marked with s) in this dicot phloem are relatively easy to recognize because they are rather large and have the typical empty appearance. However, notice that many of the cells in the cortex have a similar size and appearance. In the phloem, there are many small, cytoplasmic cells that appear to be companion cells, and these are completely absent from the cortex. In a few of the cases here, it seems possible to make a guess as to which companion cell might be associated with which sieve tube member, but it would only be a guess -- it is necessary to use transmission electron microscopy to examine the primary pit field/sieve area connections to be certain.

            This phloem also has two small secretory ducts.