THE CASTOR BEAN PLANT AND LABORATORY AIR 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 178 
E. M. HARVEY 
It is well known that the leaves of the castor bean (Ricinus 
communis) are likely to show nastic drooping after the plant has 
been brought into the laboratory. On account of the apparent 
definiteness of this response, it seemed probable that the plant 
would prove useful as a delicate test for certain gaseous impurities 
in laboratory air. It was with regard to this possibility that the 
studies reported below were undertaken. 
Potted seedlings, grown under ordinary greenhouse conditions 
until they had developed 5-7 leaves, including the cotyledons, 
were used in the tests. The pots and soil were covered with 
paraffin to avoid absorption of the gases. Exposure periods were 
all approximately 60 hours. The methods of exposure to known 
concentrations of ethylene and illuminating gas were the same 
as described by KnicHt and Crocker’ for these gases in their 
work on sweet pea seedlings. In the main, the 50-100-liter gal- 
vanized iron cans were used for exposure chambers, but, since 
here the plant would be in total darkness during the course of the 
experiment, some were exposed under bell jars provided with 
water seals and left in strong diffused light, in order to find what 
effect light would have on the sensitiveness of the response. Cor- 
responding results, however, were obtained by the two methods. 
Hluminating gas tests were run parallel with those of ethylene 
in a manner to yield evidence whether the reaction was induced 
by the ethylene constituent of the illuminating gas. Ethylene 
occurs in the Chicago illuminating gas in the concentration of 
about 4 per cent, so pure ethylene was diluted with air to 4 per cent, 
so that, volume for volume, the illuminating gas and the ethylene- 
air mixture held about the same amount of ethylene. This stock 
mixture allowed parallel experiments to be carried out readily. 
* Knicur, L. I., and Crocker, W., Toxicity of smoke. Bor. Gaz. 55:337-371- 
913. 
439] [Botanical Gazette, vol. 56 
