418 
Notes. 
THE ACTION OF LIGHT ON MESOCARPUS. — Wittrock in 
1878 first observed that the chlorophyll-plate of Mesocarpus was able 
to revolve in the cell. He did not attribute this action to light. In 
1880, Stahl published a series of papers in the Bot. Zeitung in which 
he states — 
(1) That in diffused light the chlorophyll-plate places itself at right 
angles to the incident light. 
(2) In strong sunlight the edge of the plate is turned towards the 
source of the illumination. 
(3) On continued insolation the plate — until now straight — becomes 
a curved figure. 
In 1888, S. Le M. Moore in a memoir presented to the Linnean 
Society states that — 
‘ If a specimen be so arranged that, the plate having been in full face, 
considerable approaches are making towards the profile position, 
or vice versa , on plunging now into darkness and examining after 
a short interval, the movement will be found to have been almost or 
entirely completed V 
Respecting these experiments it has been found that a very short 
light-stimulus will suffice to turn the chlorophyll-plate either from the 
vertical to the horizontal position, or vice versa. Which of these effects 
will be produced depends on the intensity of the light, though to bring 
about the complete change of position a sufficient duration of stimula- 
tion is necessary. 
A series of observations were made to determine the effect of 
stimuli of various duration, ranging from 10 seconds to one just 
sufficient to cause the plate to revolve through 90°. The experiments 
were carried out during successive days on which the intensity of the 
light was fairly constant. 
I. Experiment with diffused light ( turning the chlorophyll-plate 
from the vertical to the horizontal position ). 
In this case the Mesocarpus had been previously kept in the dark 
before being used. Cells were selected in which the chlorophyll-plates 
were vertical. A light-stimulus was then given for a definite period 
of time, and the plant (and microscope) was then darkened. In all 
cases a control-plant in continuous light was run side by side with the 
one under experiment. 
1 Journal of Linnean Soc., Bot., Vol. XXIV, p. 370. 
