Fig. 11.5-16. Transverse section of oak stem (Quercus). This is such a high magnification that the image is slightly pixelated. And even at this high magnification, it is not possible to see clearly the collapsed protophloem sieve tube members. The arrows indicate tiny dark smudges that appear to be good candidates for collapsed phloem.

            Along the outer edges of this mass of phloem are large cells that were plasmolyzed during fixation – these are the cells that would have become the phloem fiber caps.