Zea mesocotyls

[BIOHEAD]

The corn mesocotyl is the first internode of a corn seedling. Subsequent\
internodes progressively widen during establishment growth of the 
developing seedling. Prop roots emerge from nodes, most conspicuously
those above the mesocotyl. In anything larger than a seedling, the 
mesocotyl will appear as a constricted part of the shoot just below
the soil surface. Large roots circumvent this potential bottleneck
by developing above it, on larger nodes that developed after the
mesocotyl growth ceased.

A fine diagram and discussion of corn seedling development, including
the fate of the mesocotyl is found on pp 731-732 in  Foster, A.S., and 
E.M. Gifford 1974. Comparative Morphology of Vascular Plants 2nd ed.

There exists a 3rd ed., but I don't know the page numbers for that one.
Note that the original diagrams were published by the great German
morphologist, Wilhelm Troll.

Hope this helps,  George Ellmore
                  Biology Dept.
                  Tufts Univ.
                  Medford, MA