2.2. THE CASE STUDIES
35
~
f
Fig. z.ioa .b. Two photographs of the same sponge taken six months apart,
showing how the branch tips have grown : (a) The background is marked
in 2 cm squares. This sponge is a small specimen, only 5 em high. (b) The
growth of the branch tips over the six month period is shown by the numbers
(mm). The growth rate of these sponges is only 1 ern per year.
(a)
The images of the sponges were traced, and the tracings were digitized and
skeletonized using the procedure described in Sect. 3.2. The branch lengths
could then be calculated and used to determine the growth rates. An example
showing the growth of a small specimen over a three month period is given in
Fig. 2.10. By looking at these sequential photographs in detail many general
features of the growth process can be derived.
Growth is occurring only at the branch tips. Because of the spicule and
spongin skeleton it was expected that the growth of Raspailia inaequalis
would occur only at the tips of the branches. This was found to be the
case, suggesting that the growth response of only the tips needs to be
incorporated into a model.
Branching is usually symmetric. When they branch, the tips flatten and
divide symmetrically. Some tips appeared to have formed from the side
of a pre-existing branch, but this was much less common.
Branch tips turn away from the substrate. The long branch to the left of
the specimen in Fig. 2.10 is curving upwards. This was seen on a number
of specimens, and suggests that there is a vertical environmental gradient
which the sponge is able to sense and respond to.
The sponge does not rapidly turn away from itself. The small interior
branch in Fig. 2 .10 turns upwards only after it has grown into another
branch. Whatever the mechanism which controls growth , it does not
allow branches to take an advance action to avoid growing into one
another.
(b)
35
~
f
Fig. z.ioa .b. Two photographs of the same sponge taken six months apart,
showing how the branch tips have grown : (a) The background is marked
in 2 cm squares. This sponge is a small specimen, only 5 em high. (b) The
growth of the branch tips over the six month period is shown by the numbers
(mm). The growth rate of these sponges is only 1 ern per year.
(a)
The images of the sponges were traced, and the tracings were digitized and
skeletonized using the procedure described in Sect. 3.2. The branch lengths
could then be calculated and used to determine the growth rates. An example
showing the growth of a small specimen over a three month period is given in
Fig. 2.10. By looking at these sequential photographs in detail many general
features of the growth process can be derived.
Growth is occurring only at the branch tips. Because of the spicule and
spongin skeleton it was expected that the growth of Raspailia inaequalis
would occur only at the tips of the branches. This was found to be the
case, suggesting that the growth response of only the tips needs to be
incorporated into a model.
Branching is usually symmetric. When they branch, the tips flatten and
divide symmetrically. Some tips appeared to have formed from the side
of a pre-existing branch, but this was much less common.
Branch tips turn away from the substrate. The long branch to the left of
the specimen in Fig. 2.10 is curving upwards. This was seen on a number
of specimens, and suggests that there is a vertical environmental gradient
which the sponge is able to sense and respond to.
The sponge does not rapidly turn away from itself. The small interior
branch in Fig. 2 .10 turns upwards only after it has grown into another
branch. Whatever the mechanism which controls growth , it does not
allow branches to take an advance action to avoid growing into one
another.
(b)