| Lycopods are characterized by helically arranged simple leaves, usually
with a single vein, called microphylls. They bear their eusporangia on
the upper, or adaxial surface of fertile microphylls (sporophylls). Lycopodium
is a homosporous plant, that is, one with a single type of spore which
germinates to form a free living (exosporal) gametophyte that gets out
of the spore wall and lives independantly of the parent plant.
In this photo you can see a longitudinal
section through a Lycopodium cone, showing the central cone axis
surrounded by helically arranged sporophylls with sporangia on the upper
surfaces. The dark masses inside the sporangia are the spores. The sporophylls
go out beyond their sporangial attachment and turn upward forming the distal
laminae. At the base of the cone you can see some vascular tissue in longitudinal
section. The entire cone was not cut in midlongitudinal section, though,
because at higher levels you see small dots, which are the leaf traces
coming out at you in cross section. Some of the sporophylls with
their sporangia appear to be "floating" because they were cut out of the
plane of section of their attachment. |
