THE ACRASINA
(continued from vol. 2, pp. 109-182)
Β. M. SHAFFER
Department of Zoology, Cambridge University, England
V. The Grex
„
301
B. The Whole
301
C. Water as a Developmental Control
318
Summary
320
References
321
V. The Grex
B. The Whole
1. Orientation
(continued)
In the first part of this review (Vol. 2, pp. 174-5), evidence was
presented that culminating grex of Polysphondylium
violaceum orient with
respect to one another and to the substratum by steering themselves
towards lower concentrations of one of their volatile metabolites. Bonner
and Dodd (1962) have supported a similar conclusion by a great many
more observations on several species, and have also determined that the
repellent is not species specific. My other tentative conclusion that the
response is also given by Dictyostelium
discoideum slugs (and therefore
unequivocally in the lying phase) has been confirmed (Shaffer, 1962).
The basic orientation mechanism of erection remains obscure.
Lower plants being fairly transparent, their phototropism is in
general due to a lens effect (Blaauw, 1918; Castle, 1933), parallel light
striking one side of a uniform cylindrical body being focused by it and
thus absorbed to a greater extent in its more distant half. Consequently,
if only half of it is illuminated, the cylinder behaves as if all of it were lit
by light entering through the opposite half; and if movement is normally
towards light, half illumination induces motion out of the path of the
light and perpendicular to it (Buder, 1920). Francis (1962) has obtained
just such an effect when light is shone down onto one side of the tip of a
D. discoideum
slug, which is positively phototactic (Raper, 1940;
Bonner et ah, 1950), and he has also determined the action spectrum of
phototaxis.
Exactly how differential light absorption makes the slug tip turn is
301
(continued from vol. 2, pp. 109-182)
Β. M. SHAFFER
Department of Zoology, Cambridge University, England
V. The Grex
„
301
B. The Whole
301
C. Water as a Developmental Control
318
Summary
320
References
321
V. The Grex
B. The Whole
1. Orientation
(continued)
In the first part of this review (Vol. 2, pp. 174-5), evidence was
presented that culminating grex of Polysphondylium
violaceum orient with
respect to one another and to the substratum by steering themselves
towards lower concentrations of one of their volatile metabolites. Bonner
and Dodd (1962) have supported a similar conclusion by a great many
more observations on several species, and have also determined that the
repellent is not species specific. My other tentative conclusion that the
response is also given by Dictyostelium
discoideum slugs (and therefore
unequivocally in the lying phase) has been confirmed (Shaffer, 1962).
The basic orientation mechanism of erection remains obscure.
Lower plants being fairly transparent, their phototropism is in
general due to a lens effect (Blaauw, 1918; Castle, 1933), parallel light
striking one side of a uniform cylindrical body being focused by it and
thus absorbed to a greater extent in its more distant half. Consequently,
if only half of it is illuminated, the cylinder behaves as if all of it were lit
by light entering through the opposite half; and if movement is normally
towards light, half illumination induces motion out of the path of the
light and perpendicular to it (Buder, 1920). Francis (1962) has obtained
just such an effect when light is shone down onto one side of the tip of a
D. discoideum
slug, which is positively phototactic (Raper, 1940;
Bonner et ah, 1950), and he has also determined the action spectrum of
phototaxis.
Exactly how differential light absorption makes the slug tip turn is
301