Fig.
8.2-8.
High magnification of cucumber phloem. This micrograph has a prominent sieve
plate and P-protein plug, but also shows that sieve
tube members can have multiple companion cells. Each pair of arrows
indicates the two companion cells for one sieve tube member (the lower pair of
arrows lies in the sieve tube member; the two upper companion cells are
associated with the cell just above them and almost out of view). In this
species we see companion cells side by side, but in other species, a sieve tube
member might be accompanied by a row of companion cells in a linear arrangement
down one side.