- Many of the mathematical recipes here in the Kitchen are motivated by
real-world phenomena, so it is especially affirming when a physical system
produces patterns and dynamics that are the spitting image of a CA rule.
One celebrated biological example of an excitable medium is the early
aggregation phase of amoebae in the surreal life cycle of a slime mold
known as Dictyostelium discoideum, or Dicty for short. This
week's soup is a colorized scan of spiral patterns generated during that
phase. A little Web surfing reveals an active cadre of Dicty fanatics,
seemingly concentrated in Germany and Texas. So here are some particularly
interesting and amusing links to their arcane subculture.
- For starters, a capsule summary by La Trobe University
Microbiologist Paul Fisher (fisher@lumi.latrobe.edu.au):
- Dictyostelium discoideum is a cellular slime mould whose natural habitat
is soil and leaf litter where it predates bacteria by phagocytosis, grows
and divides by mitosis. The Dictyostelium discoideum life cycle begins
with differentiation of starving amoebae to a form where they become
capable of synthesizing, secreting and being attracted by extracellular cAMP.
The resulting aggregation process forms a multicellular migratory organism,
the "slug", which migrates through a cellulose/protein extracellular matrix,
the "slime sheath", that collapses behind to form a trail. Slugs are
phototactic, thermotactic and weakly chemotactic. After a variable period
of migration the slug stops and forms a fruiting body consisting, to a first
approximation, of a droplet of spores supported by a tapered stalk and
basal disc.
- There is
The Munich Dicty Site, a source of great little movies depicting the aggregation
phase. We have lifted three of these which are quite reminiscent of
our previous CA recipes for macaroni,
multistrand spirals and spiral cores,
respectively. Those of you with mpeg viewers can click on the thumbnails below to
download and view the sequences:
 Macaroni movie
 Multistrand spiral movie
 Spiral Core movie
- Another hotbeds of slime is:
 The Rice Dicty Site
- (Eugenio has a Power Mac named Dicty, and offers a .mov flick for the
Apple crowd).
- But surely the preeminent archive of Slime Mold wisdom is
The Dicty Web Server
- with an extensive bibliography, info on upcoming scientific get-togethers, lots of group
snapshots, an email mailing list, and even some great sequences of
Dicty Genetic Code.
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