. Botany of the living plant. Botany; Plants. GROWTH, IRRITABILITY AND MOVEMENT 145 9 - ' &V Cito^-** /O. 30 /o ro is required. Thus we can measure increase in linear dimensions, in volume, or in weight : the impression that is gained of the growth of a plant or organ is, however, liable to vary according to the particular index of growth that is adopted. The growth of a root or a stem is usually measured by noting the increase in length over a given time. For this purpose the horizontal microscope, of which different patterns are available, may be employed, or one may use the anxano- mete
. Botany of the living plant. Botany; Plants. GROWTH, IRRITABILITY AND MOVEMENT 145 9 - ' &V Cito^-** /O. 30 /o ro is required. Thus we can measure increase in linear dimensions, in volume, or in weight : the impression that is gained of the growth of a plant or organ is, however, liable to vary according to the particular index of growth that is adopted. The growth of a root or a stem is usually measured by noting the increase in length over a given time. For this purpose the horizontal microscope, of which different patterns are available, may be employed, or one may use the anxano- meter, in which the growth is magnified by means of levers or pulleys for the purpose of measurement. If the growth of the plant as a whole is required it is usual to observe the increase in its weight. A special value as a growth- index has been placed on the dry weight of the plant, the weight of matter remaining after the water originally present has been driven off by drying the plant tissues in an oven. What this method measures is the net amount of environmental mater- ial that has been incorporated into the actual substance of the plant, irrespective Of whether Record of circumnutation in a seedling made by • . , . , , . Malins Smith. Note that the direction was reversed this has been USed tor growth Or before in this record. deposited as a storage material. The determination of dry weight involves killing a plant, so that consecutive observations cannot be made on a single plant : a series of similar plants must be available when growth is to be measured in this way. (c) Factors affecting Growth. Since in its growth the plant utilises the products of its assimilatory processes, such as the synthesis of carbohydrate and of protein, it is obvious that factors affecting those processes may also affect growth. Thus growth will be hindered if adequate supplies of raw materials such as carbon dioxide, water and nutrient salts are not to hand: experiments indicatin
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