1314 
for instance in the case of most of vAN SLOGTEREN’s experiments. 
That is why measures such as the use of the large-surface-chambers 
ern ee emt er 
Photo J. QUELLE. 
Fig. 5. Arrangement of the recording apparatus. To the left the recording 
drum and in front of it one of the two writing clockworks (U2). The second 
clock conformable to the first was too much to the left to be seen in the 
photo only some parts belonging to it (112, 12e, 15) are visible. The clockwork 
moving the drum should also be thought to the left. To the right the two 
automatic mercury switches (the one in front of the other) and behind those 
a resistance. Further explanation of the figures in the text. 
and the diminution of the gas-contents of the porometer are to be 
recommended. 
The fixing of the chamber to the leaf remains a difficult question. 
In 1914, when I was occupied with ordinary porometer-observa- 
tions, I tried a number of glues, and just as VAN SLOGTEREN '), | 
came to the conclusion, that ordinary Arabic gum is by far the best. 
In 1919 on the advice of my colleague J. Heimans, I tried mixing 
a small quantity of Sesame-oil with the gum and indeed this makes 
the substance somewhat tougher and cracks do not so soon appear 
in drying. Besides [ always add a trace of Thymol, to prevent its 
decay. Too much thymol is injurious to the experimental plant. 
1) Le, p. 20. 
