Internode
Lengths of
Silvetia compressa (J. Agardh)
Serrão, Cho, Boo et
Brawley
(which used to be called Pelvetia)
It was found that internode lengths varied significantly (95% confidence) among
the three sites. Most noticeable was that plants at Pt. Pinos had internodes
almost twice those at Hopkins Marine Station. It is hypothesized that the
longer internodes are created when branches break off due to wave forces.
This sort of pruning may serve as an adaptation to wave forces. By pruning,
a plant may reduce its area. Since the drag force (a hydrodynamic force)
is proportional to area, pruning may help the thallus to decrease drag forces.
Click below to view the branch after pruning.
Pruning could reduce drag force if the plants do not regain the pruned area by growing more at the tips of the plants. If the Pt. Pinos plants indeed lose area by pruning, their ratios of area per length will be less than those of Hopkins plants. This was found to be true; therefore, it is likely that the longer internodes at Pt. Pinos are related to pruning as a way to reduce wave forces on a thallus.
© 1996 R. H. Lin