| Here are some Isoetes leaves in transverse section. You can
see that they are helically arranged. Each leaf shows a single central
vascular bundle and four large air spaces in very simple mesophyll.
The leaves to the outside have a little laminar tissue on either side that
make up a sheath, but it looks like it is only a cell or so thick. Remember,
many Isoetes plants are aquatic or semiaquatic, and the air channels
help keep the leaves oxugenated. Remember too, leaves of Isoetes
are typically fertile, so at other levels these leaves probably either
develop or bear sporangia on their adaxial surfaces. What other feature
would you expect in these leaves if you cut them at the proper level? |
