SACHS’S IODINE EXPERIMENT (JODPROBED 
TRIED IN THE TROPICS. 
BY 
J. C. COSTERUS. 
At the suggestion of Dr. M. Treub, Director of the Botan- 
ical Gardens at Buitenzorg (Java) I devoted part of the time, 
I spent in the isle of Java in 1892, to some observations as 
to the quantity of amylum contained in leaves at different 
times of the day and under varying influences of bright and 
dull weather. For my purpose I always used plants in full 
ground and open air. The regularity shown by the changes of 
weather was likely to afford a favourable opportunity for ob- 
taining some more details about the process of assimilation , 
and some reliable data towards solving the problem how great 
the production by a leaf would be under the influence of trop- 
ical heat and blazing sunshine. 
The temperature during night at Buitenzorg is from 21° to 
22° C.; in the daytime it rises about 8 degrees in the shade, 
in the direct sunshine still more. The sun rises at six o’clock 
or a few minutes before and is not much more than 12 hours 
above the horizon, the twilight is of very short duration. In 
the first days of my sojourn (February—June) rain set in 
between 1 and 2 o’clock, but afterwards the rain came grad- 
ually later, until in the last few weeks of my stay it did 
not set in before 5 or 6, and on a few days stayed away 
altogether. : 
