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Rh pressure of their own weight. The excursion of the end of the recording lever, which represents magnified movement of growth, was now found to be without jerk and quite uniform.

The soil in a flower pot is liable to be disturbed by irrigation, and the record thus vitiated by physical disturb- ance. This is obviated by wrapping a piece of cloth round the root imbedded in a small quantity of soil. The lower end of the plant is held securely by a clamp. In order to subject the plant to the action of gases and vapours, or to variation of temperature it is enclosed in a glass cylinder (V) with an inlet and an outlet pipe (Fig. 58). The chamber is maintained in a humid condition by means of a sponge soaked in water. Different gases, warm or cold water vapours, may thus be introduced into the plant chamber.

Any quick growing organ of a plant will be found suitable for experiment. In order to avoid all possible disturbing action of circumnutation, it is preferable to era- ploy either radial organs, such as flower peduncles and buds of certain flowers, or the limp leaves of various species of grasses, and the pistils of flowers. It is also advisable to select specimens in which the growth is uniform. I ap- pend a representative list of various specimens in which, under favourable conditions of season and temperature, the rates of growth may be as high as those given below : —

Peduncle of Zephyranthes ... ... 0'7 imii. per hour.

Leaf of grass ... ... .1’10 ,, „ ,,

Pistil oi. Hibiscus flower ... ... 1'20 „ ,, ,,

Seedling of wheat ... ... ... 1 '60 ,, ,, ,,

Flower bud of Crinum ... ... 2"20 „ ,, ,,

Seedling of Scirpus Kysoor ... ... 300 „ ,, ,,