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seen in the middle record of Fig. 68b, where the rate is seen to be double the normal. Continued action, however, caused a depression; the third record of this series shows this, where the reduction is three-fourths of the normal rate.

Ether: Experiment 64.—In Fig. 68c, the records exhibit the effect of introduction of ether vapour into the plant chamber, and its recovery after the removal of the vapour. Ether is seen to depress the rate of growth to a little more than a third of the normal rate. The recovery is seen to be nearly complete half an hour after the removal of the vapour.

Carbonic Acid: Experiment 65.—The action of this gas is very remarkable. The plant was immersed in water and normal record taken;
Fig. 69.—Effect of CO₂. (a) Normal record; (b) immediately after application of CO₂ and (c) 15 minutes after. the plant chamber was now filled with water, charged with carbonic acid gas. This induced a very marked acceleration of growth (Fig. 69). In a seedling of Onion, the increase was found to be two and a half times. In the flower bud of Crinum, the rate was found enhanced threefold from the normal 0.25 μ to 0.75 μ per second. After this preliminary enhancement, there was a depression of growth within 15 minutes of the application, the