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F. C. Newcombe 
the vaseline, growth ceased without any curving, and the shoots, 
after a day or two, sagged of their own weight. There was never in 
any of the plants a curve that could be called geotropic. 
Series III. In carbon dioxide atmosphere. The seedlings used in 
this series were all grown in small crystallising dishes in earth, and 
the dishes with their seedlings were placed in the experimental 
chambers when the shoots had grown from i to 5 cm. above ground. 
All preparations were kept in the dark. The culture chambers were 
belljars of 10 litres capacity with tubulature at the- top. The jars 
stood in large basins holding water, the crystallising dishes on 
supports above the water. The belljars were graduated, and a 
graduated scale was fastened to the side. An aspirator connected 
with the culture chambers enabled one to fill the chambers with 
water to any desired height. The carbon dioxide was let into the 
chambers from a reservoir or directly from a generator after washing 
the gas. The water used in the culture chambers was drawn from a 
small closed tank which contained carbon dioxide in the same con¬ 
centration as that to be used in the culture chambers. Thus there 
could be but small exchange of gases between the water and the gas 
in the culture chambers. To control the percentage of carbon dioxide 
rather closely, a small quantity of gas was drawn from the culture 
chamber both just before and just after an experiment, and the 
amount of carbon dioxide determined by titration. Usually there 
was an increase of 2 to 4 per cent, in the concentration of the carbon 
dioxide during the progress of an experiment, due to the respiration 
of the seedlings. Concentrations of carbon dioxide from 4 to 75 
per cent, were used, the most of the seedlings having 10 to 20 per 
cent. 
One hundred and twenty-five seedlings of Helianthus annuus were 
used, and, besides these, 16 of Lupinus albus, 13 of Pisum sativum, 
and enough of Phaseolus vulgaris L., Cucurbita maxima, Brassica 
alba Boess., Zea mais and Avena sativa to bring the total to 250 
seedlings. 
None of the seedlings showed reverse curves. The Helianthus 
shoots made upward curves in all the percentages of carbon dioxide 
used—from 4 to 20 per cent. Lupinus bent its hypocotyl upward in 
20 and 50 per cent.; older seedlings of Phaseolus bent the epicotyl 
upward while the mature hypocotyl remained straight; Pisum 
epicotyls bent sharply upward in 12 and 20 per cent.; Cucurbita 
bent slightly upwards in 33 per cent.; Brassica did not grow but lost 
its turgidity and sagged down in 75 per cent.; Zea had unfolded its 
first leaves when placed in an atmosphere of 35 per cent., but made 
slight upward bends—about the same behaviour as shown by 
controls. 
