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On the Effect of Carbon Diomde on Geotropic Curvature of the 
Roots of Pisum sativum L. 
By Eric DrasBstE, D.Sc., F.L.S. (Demonstrator in Botany, Royal 
College of Science), and HitpA LAKE. 
(Communicated by J. Bretland Farmer, F.R.S. Received May 12,—Read 
June 8, 1905.) 
Introductory. 
Many physiologists have shown that, in general, carbon dioxide exercises 
a narcotic or toxic influence on vegetable protoplasm, temporarily or per- 
manently affecting its activity, according to the partial pressure under which 
the gas acts. De Saussure (1), as long ago as 1804, stated that, in an atmos- 
phere containing 8 per cent. carbon dioxide, the growth of peas was less than 
in air; Bohm (2), in 1873, found that roots of Phaseolus multiflorus, after 
17 days’ exposure, exhibited successively less elongation in partial pressures 
of 2, 5, 10, and 14 per cent. carbon dioxide respectively, the temperature 
ranging between 17° and 19° C.; in each percentage named the growth was 
progressively less than in normal air. Montemartini (3), in 1892, working 
with roots of Pisum, found 7 per cent. and upwards to depress growth- 
activity. Chapin (4), in 1902, found the growth of roots of Piswm sativum 
and Vicia sativa to be diminished by 5 per cent., and arrested by 25 to 
30 per cent. and upwards. Growth of the stem in the same plants was 
diminished by 15 per cent., and completely inhibited by 22 to 25 per cent. 
‘Experiments conducted by one of us, in conjunction with Professor Farmer, 
have proved that seedling peas may be kept in an atmosphere containing 
20 per cent. carbon dioxide for 14 days without losing the power of renewed 
growth when placed in air. It is interesting to note that, in many of these 
plants, the plumule was destroyed, although the main root continued to 
grow, growth being carried on by shoots arising in the axils of the cotyledons. 
Brown and Escombe (5) grew plants in increased partial pressures of 
carbon dioxide. The anatomy of these plants was investigated by Farmer 
and Chandler (6), who found the growth of the aérial parts to be diminished, 
while root-growth was apparently unaltered. Ewart (7) observed that 
carbon dioxide stops protoplasmic streaming, but he does not state the 
percentage employed in his experiments. | 
Professor J. B. Farmer and Dr. A. D. Waller, as the result of a series of 
experiments on the action of various substances on protoplasmic streaming in 
Elodea and Chara, observed that, after treatment with carbon dioxide for a 
