6. PHOTOTROPISM AND PHOTOTAXIS
245
sur le cöte le moins eclaire de ce verre, et le cote qui etoit tourne vers
le jour n'en avoit que quelques uns. II s'agissoit done de voir, si le
grand nombre de Polypes passeroit du cote le moins eclaire, sur le cöte
le plus eclaire. Le jour apres avoir tourne le verre, je trouvai que le
cöte le moins eclaire, celui sur lequel j'avois laisse beaucoup de Polypes,
en etoit presque entierement depeuple. Ils etoient disperses dans le
verre, et en chemin pour se rendre sur le cöte du verre le plus eclaire;
car le lendemain j'y en trouvai deja plusieurs, et au bout de quelques
jours, il y en eut autant qu'il y en avoit sur l'autre, avant que j'eusse fait
faire un demi tour au verre. . . . Apres avoir vu la meme chose
plusieurs fois, je fus convaincu que les Polypes avoient un penchant
particulier pour Tendroit du verre le plus eclaire." Subsequently he
made more elaborate experiments with a chevron-shaped slit in a cardboard box, always finding the polyps assembled in a chevron-shaped
group opposite the slit. Furthermore, the effect could not be due to
warmth, for if the slit were turned towards the stove they did not assemble there,—only if it were turned towards the window. Hence he
concluded, "II paroit done certain que e'est en effet la lumiere qui attire
ces Animaux sur le cöte du verre le plus eclaire." Trembley also recognized that this attraction towards light is a very general phenomenon,
and instances flies, moths, butterflies, etc., being attracted by lamps
on summer evenings, as well as Adriatic fishermen who go out to catch
marine polyps at night with a bright light above the water. This latter
practice is, of course, common in the Mediterranean to this day.
The middle of the 19th century saw an increasing number of experiments, especially on animals, but it was the extensive studies of
Jacques Loeb, beginning in 1888 and continuing for nearly 30 years,
which brought out most of the characteristics of the light responses of
animals.
Meanwhile the beautiful experiments of Engelmann on phototaxis
of purple bacteria were so advanced for their time, 1882-1888, that they
lay neglected for many years. Later they were taken up first by Oltmanns and then, over a period of years, by Mast, working with both
plants and animals. However, phototaxis has never had quite the intensive study it deserves.
In higher plants the early botanists had ascribed phototropic curvatures to heating or to increased loss of water on the lighted side, and it
was Darwin, Rothert, and others in the late 19th century who made
these naive explanations impossible by using very photosensitive seedlings which could be exposed to low light intensities for short durations.
Finally Blaauw, in the period 1908-1918, with his careful calibration
of the light energy and precise, extensive observations, did essentially
245
sur le cöte le moins eclaire de ce verre, et le cote qui etoit tourne vers
le jour n'en avoit que quelques uns. II s'agissoit done de voir, si le
grand nombre de Polypes passeroit du cote le moins eclaire, sur le cöte
le plus eclaire. Le jour apres avoir tourne le verre, je trouvai que le
cöte le moins eclaire, celui sur lequel j'avois laisse beaucoup de Polypes,
en etoit presque entierement depeuple. Ils etoient disperses dans le
verre, et en chemin pour se rendre sur le cöte du verre le plus eclaire;
car le lendemain j'y en trouvai deja plusieurs, et au bout de quelques
jours, il y en eut autant qu'il y en avoit sur l'autre, avant que j'eusse fait
faire un demi tour au verre. . . . Apres avoir vu la meme chose
plusieurs fois, je fus convaincu que les Polypes avoient un penchant
particulier pour Tendroit du verre le plus eclaire." Subsequently he
made more elaborate experiments with a chevron-shaped slit in a cardboard box, always finding the polyps assembled in a chevron-shaped
group opposite the slit. Furthermore, the effect could not be due to
warmth, for if the slit were turned towards the stove they did not assemble there,—only if it were turned towards the window. Hence he
concluded, "II paroit done certain que e'est en effet la lumiere qui attire
ces Animaux sur le cöte du verre le plus eclaire." Trembley also recognized that this attraction towards light is a very general phenomenon,
and instances flies, moths, butterflies, etc., being attracted by lamps
on summer evenings, as well as Adriatic fishermen who go out to catch
marine polyps at night with a bright light above the water. This latter
practice is, of course, common in the Mediterranean to this day.
The middle of the 19th century saw an increasing number of experiments, especially on animals, but it was the extensive studies of
Jacques Loeb, beginning in 1888 and continuing for nearly 30 years,
which brought out most of the characteristics of the light responses of
animals.
Meanwhile the beautiful experiments of Engelmann on phototaxis
of purple bacteria were so advanced for their time, 1882-1888, that they
lay neglected for many years. Later they were taken up first by Oltmanns and then, over a period of years, by Mast, working with both
plants and animals. However, phototaxis has never had quite the intensive study it deserves.
In higher plants the early botanists had ascribed phototropic curvatures to heating or to increased loss of water on the lighted side, and it
was Darwin, Rothert, and others in the late 19th century who made
these naive explanations impossible by using very photosensitive seedlings which could be exposed to low light intensities for short durations.
Finally Blaauw, in the period 1908-1918, with his careful calibration
of the light energy and precise, extensive observations, did essentially