ADAPTATIONS OF GYMNOSPERMS TO SURVIVAL ON DRY LAND
Vascular tissue: Allows gymnosperms to draw water from the ground via a system of
xylem which connects the roots to the leaves.
Seeds: Surrounded by a desiccation-resistant seed coat. They can last for years, in some
cases, and germinate when water becomes available.
Pollen: This is the male gametophyte wherein the male gamete – the sperm nucleus – will
develop. Pollen grains have no flagella because, rather than swimming to find a
female gamete, they are borne on the wind in immense numbers. Furthermore,
pollen grains have a thick coat which is resistant to water loss.
Needles: Gymnosperm species which have needle leaves are especially resistant to
desiccation. The openings (stomata) on the needles of a pine are located in sunken
pits. This allows for a tiny region where water escaping the leaf remains in
relatively high concentration, in comparison to the surrounding atmosphere. This
limits water loss a great deal. In addition, needles are surrounded by a thick layer
of epidermal cells, covered by a waxy cuticle.
Alternation of generations:
 The gametophyte generation is very small. In conifers, the female gametophyte is
well protected within an ovule within the scales of the cones. The male
gametophyte is similarly protected within the male cone; then within the female
cone as it develops a pollen tube and fertilizes the female egg. Because the
gametophytes are so well protected there is little chance of their drying out.
Furthermore, the male gamete is not a flagellated sperm which has to swim, but
one which gets to the female gamete via pollination (wind dispersal followed by
growth of a pollen tube), so water is not necessary.
 The large, visible generation of gymnosperms is the sporophyte – what we
commonly call trees. These grow from desiccation-resistant seeds and soon
develop into hardy plants with the amazing specializations discussed above
(vascular tissue, needles).
 Some biologists also think that it is genetically advantageous to have the diploid
stage as the main, long-lasting stage in the life cycle. Since trees have two sets of
each chromosome, inherited weaknesses and deleterious mutations on one
chromosome are, in part, ‘covered up’ by the other chromosome. In this way,
the forest population maintains a rich genetic diversity, which may prove
beneficial should environmental conditions change in the future.
(© 2004. C.K. Robinson, Summerland Community Learning Centre, School District No. 67)