Physiological Botany by Unknown

Author:Unknown
Language: eng
Format: epub

146

1 For a full account of its construction see AiHiales des Sc. nat., ser. 6, tome vi., 1378, p. 186.

2 Botanisehe Zeitung, 1878, p. 161.

' A simpler piece of apparatns arranged by Pfeffer answers well for class demonstration. It is easily understood from Fig. 147. The fall of water in the small lateral tube is very marked, hut attention should be called to the varying pressure caused by the constantly changing level of the water in the tube.

Fig. 116. Krntl sky's apparatus.

Digitized by VjOOQlC

274 TRANSFER OF WATEB THROUGH THE PLANT.

drops. This method of demonstrating transpiration has been used, when somewhat modified, by many investigators, notably Deherain. 1 It is well adapted to class experiments, since veiy simple appliances 2 can be used: for instance, a leafy stein can be inserted in a piece of pasteboard, and the cut end of the stem placed in a tumbler of water; another tumbler, inverted over the stem, rests on the pasteboard. The water in the lower tumbler is prevented from evaporating into the upper one. The amount of water which collects on the inside of the upper tumbler comes wholly from the transpiration of the plant, and will be found to vary according to the surroundings (see page 275 et seq).

736. If a neighed amount of calcic chloride is placed! with a transpiring plant in a confined Atmosphere, the salt will readily take up the aqueous vapor, and its increase in weight gives the amount of water exhaled by the plant. This method of measuring the amount of transpiration has been employed by several experimenters, who have obtained results substantially in accord. It must be noted, however, that in this method the air to which the plant is exposed is rendered abnormally drj* by the presence of the salt, and the plant is therefore subjected to an unusual draft upon its water-supply.

737. Garreau's method of comparing the relative amounts of transpiration on opposite sides of a leaf is based on that last

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