There are two basic types of Plant Sperm. Some are biflagellate and others are multiflagellate.
This is an over-simplification but it is enough for the present to recognize this
disparity in reproductive cells.
Model
of Bryophyte Sperm which has two Flagella
Model
of Fern-Type Sperm which has many Flagella!!!
Evolutionary Biologists place a lot of
emphasis on the traits of sperm because changes in a central component of the reproductive
system are thought to be more important than a change in the complexity of epidermal hairs
for instance. A change in sperm motility signals a significant departure from the
evolutionary trajectory of a taxon.
There are other important sperm modifications that
we will observe later. Some terrestrial plants have
enormous sperm with thousands
of flagella. However, this
taxon (Cycadophyta) is almost extinct! Size isn't
everything! They have the largest Cones and Seeds too! It is often the most simple design that wins the race.
Eventually, we will see that the sperm of flowering
plants lack flagella and are not motile.
The presence of flagella indicates that the Sperm is
designed to swim through water to achieve Syngamy. This is clearly a disadvantage on dry
land.
