The reagent, when in a liquid form, is locally applied on the growing organ. The records, taken before and after the application, exhibit the stimulatory or depressing character of the reagent. A different method of application of the reagent is employed for plants with extended region of growth. The specimen is then enclosed in a glass cylinder, with inlet and outlet pipes. The cylinder is first filled with water, and the normal rate of growth recorded. This rate remains constant for several hours; but prevention of access of air for too long a time affects the normal growth. After obtaining normal record, water charged with the giving chemical agent is passed into the cylinder; and the subsequent record shows the characteristic effect of the reagent. The introduction of a gas into the chamber offers no difficulty. EFFECT OF STIMULANTS. _Hydrogen Peroxide: Experiment 62._--This reagent, as supplied by Messrs. Parke Davis & Co., was diluted to 1 per cent. and applied to the growing plant. Its stimulating action on growth is demonstrated in the right hand record of Fig. 68_a_, where the rate of growth is seen enhanced two and a half times the normal rate. [Illustration: FIG. 68.--Effect of chemical agents: (_a_) Acceleration of growth under H_{2}O_{2}, (_b_) Effect of NH_{3}, preliminary acceleration followed by retardation. (_c_) Effect of ether (E) and recovery (A).] _Ammonia: Experiment 63._--The immediate effect of dilute vapour of this reagent is an enhancement of growth, seen in the middle record of Fig. 68_b_, 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. EFFECT OF ANÆSTHETICS. [Illustration: FIG. 69.--Effect of CO_{2}. (_a_) Normal record; (_b_) immediately after application of CO_{2}, and (_c_) 15 minutes after.] _Ether: Experiment 64._--In Fig. 68_c_, 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; 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 rate being now reduced to 0.15 µ per second. These effects were found to take place equally in light or in darkness. ACTION OF DIFFERENT GASES.