Physiologie. 
655 
titative Bestimmungsmethode des Dipsacans fehlte, aber die Intensität 
der blauen Farbe, welche die Pflanzenteile bei Erwärmung im feuch¬ 
ten Raume erhalten, war hinreichend zur vorläufigen Bestimmung, 
der Lokalisation und der Quantität. Das Dipsacan kommt innerhalb 
der Zelle, nicht in der Zellwand vor und findet sich in allen Orga¬ 
nen und allen Geweben, ausgenommen in dem Marke des Stengels. 
Die Menge hängt von den Wachstumsbedingungen ab, unter 
ungünstigen Umständen ist der Gehalt geringer, der grösste Gehalt 
findet sich jedoch immer in den wachsenden Teilen; durch Ver¬ 
dunklung der Blätter ist sogar nach einigen Wochen keine Vermin¬ 
derung zu beobachten. Die Familie der Dipsaceae, in sämtliche 
darauf untersuchten Gattungen und Arten wird durch den Besitz 
des Dipsacans charakterisiert, es sind jedoch die Dipsacus -Arten am 
Dipsacanreichsten. Th. Weevers. 
Went, F. A. F. C , On the investigations of Mr. A. H. Blaauw 
on the relation between the intensity of light and the 
length of illumination in the phototropic curvatures in 
seedlings of Avena sativa. (Kon. Ak. Wet. Amsterdam. Proc. 
Meetk. Sept. 26. 1908.) 
In none of the investigations of Wiesner, Figdor and Czapek 
an attempt has been made to ascertain, whether there is a con- 
nexion between the presentation-time and the intensit}^ of light. The 
author placed the plants at various distances from the source of 
light, they were illuminated for a given time, then left in the dark 
and were examined for phototropic curvature after about two hours. 
The intensity of light was varied in different manners (from 0.000439 
Hefner candles tili 26520 H. c.) and measured by means of a Weber 
photometer. The period of illumination varied from 13 hours to 
0,001 second, which very short periods were obtained by means of 
a photographic instantaneous shutter with slit. 
While the presentation-time was assumed by Czapek to be 7 
minutes, Mr. Blaauw in his experiments still obtained a reaction, 
when the exposure was diminished to 0,001 second, provided the 
light was very strong. 
With a longer exposure the strength of the light may be dimi¬ 
nished and still a curvature may be obtained, but this fact may be 
expressed much more exactly in the following way, when we com- 
pare the products of the lenght of the exposure and the correspon- 
ding intensity of light in H. c., which just suffices for a phototropic 
reaction. 
The interesting result is, that these products are nearty iden- 
tical. Perfect identity cannot be expected in experiments of this 
nature, but they oscillate about a mean. In other words w T e may 
conclude that a definite quantity of light is required to produce a 
reaction. The essential condition for the production of a phototropic 
curvature is therefore the supply of definite quantity of radiant 
energy and whether this quantity is supplied in a short or a long 
time is a matter of indifference. 
Bloch and Charpentier obtained similar results when obser- 
ving the reaction of the human eye and from observations published 
by Bach we may perhaps deduce that something of the same na¬ 
ture holds good for geotropic curvatures. • Th. Weevers. 
