176
B. M. S H A F F E R
has yet to be examined; possibly the grex respond to something quite
simple. But preliminary indications are that it is neither basic nor
acidic; for Bonner and Shaw (1957) in their experiments on humidity
reported that D. mucoroides grex were not attracted towards sulphuric
acid, and I have found that even in coverslip chambers of small volume
P. violaceum grex are not obviously deflected towards acid, alkali, or a
specific absorbent of ammonia.
In Polysphondylium, rings of cells, pinched off from the hind end of
the standing grex, are left behind at intervals along the stalk. Each
ring then forms a whorl of small fruiting bodies essentially of the Dietyostelium type, in a plane perpendicular to this stalk. We need not
suppose, as Harper (1929) did, that the developing branches show new
tropisms: the mutual repulsion of the daughter grex can here reinforce
the ordinary erection mechanisms. Very similarly, a spherical aggregate
of D. discoideum taken from suspension at a sufficient age not to disperse in contact with a substratum, and deposited in the mesh of a gauze
net, often produces an erect fruiting body from each side (Gerisch,
1960).
Before any stalk is formed, the grex of D. polycephalum may divide
longitudinally into as many as ten daughters (Fig. 21). These then construct fruiting bodies of the normal Dictyostelium pattern, except that
when finished their stalks are closely appressed for the lower threequarters of their length and diverge sharply at a point corresponding to
the start of spore encapsulation (Figs. 23, 24; Raper, 1956b). Because
very little slime-sheath material would be produced after this differentiation, Bonner (1959a) argued that the main factor in drawing the
stalks together was the mutual adhesion of the slime sheaths that had
FIGS. 21 to 24. Culmination in D. polycephalum (Raper, 1956a, b). FIG. 21. A single
grex has divided into a number of erect daughters. FIG. 22. A later stage of a different
group. The component grex have diverged, but not separated. FIG. 23. Mature fruiting
bodies with spherical masses of spores at the tips of the stalks. FIG. 24. A mature fruiting
structure to show the cellular stalks and their slight divergence at the base as well as at
the tip.
B. M. S H A F F E R
has yet to be examined; possibly the grex respond to something quite
simple. But preliminary indications are that it is neither basic nor
acidic; for Bonner and Shaw (1957) in their experiments on humidity
reported that D. mucoroides grex were not attracted towards sulphuric
acid, and I have found that even in coverslip chambers of small volume
P. violaceum grex are not obviously deflected towards acid, alkali, or a
specific absorbent of ammonia.
In Polysphondylium, rings of cells, pinched off from the hind end of
the standing grex, are left behind at intervals along the stalk. Each
ring then forms a whorl of small fruiting bodies essentially of the Dietyostelium type, in a plane perpendicular to this stalk. We need not
suppose, as Harper (1929) did, that the developing branches show new
tropisms: the mutual repulsion of the daughter grex can here reinforce
the ordinary erection mechanisms. Very similarly, a spherical aggregate
of D. discoideum taken from suspension at a sufficient age not to disperse in contact with a substratum, and deposited in the mesh of a gauze
net, often produces an erect fruiting body from each side (Gerisch,
1960).
Before any stalk is formed, the grex of D. polycephalum may divide
longitudinally into as many as ten daughters (Fig. 21). These then construct fruiting bodies of the normal Dictyostelium pattern, except that
when finished their stalks are closely appressed for the lower threequarters of their length and diverge sharply at a point corresponding to
the start of spore encapsulation (Figs. 23, 24; Raper, 1956b). Because
very little slime-sheath material would be produced after this differentiation, Bonner (1959a) argued that the main factor in drawing the
stalks together was the mutual adhesion of the slime sheaths that had
FIGS. 21 to 24. Culmination in D. polycephalum (Raper, 1956a, b). FIG. 21. A single
grex has divided into a number of erect daughters. FIG. 22. A later stage of a different
group. The component grex have diverged, but not separated. FIG. 23. Mature fruiting
bodies with spherical masses of spores at the tips of the stalks. FIG. 24. A mature fruiting
structure to show the cellular stalks and their slight divergence at the base as well as at
the tip.