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Fig. 7.2-8. Longitudinal section of vessel element of corn (Zea mays). Corn is a flowering plant (as opposed to a conifer), so its circular bordered pits are small, like those of American hornbeam in Fig. 7.2-7, rather than large like those of pine in Fig. 7.2-6. Notice that these circular bordered pits are not quite as orderly as the ones in American hornbeam; they are of various sizes, some quite a bit larger than others, and they do not form a neat hexagonal arrangement. The regularity of pitting is variable – in some species, scalariform pits or circular bordered pits are remarkably regular; in others, they are almost haphazard.

            The four thick red bands on the right are pieces of annual secondary wall on an adjacent vessel element. They are slightly out of focus, indicating that the cell they and their associated cell are lying slightly above or below the pitted wall. Notice that there is a nucleus at the lower arrow; it is lying in (or beside) a long cell whose end wall is visible at the upper arrow. Because we can see the end wall, it is probably lying above the annular wall; if it were below it, the annular wall is so dense it would probably hide the end wall.