Meetings of the Botanical Society

In plants the roots are supplying many essentials for shoot growth among which water and minerals are quantitatively the most important. In addition specific substances (e.g. hormones) are produced by the root system. The function of the shoot is to supply the roots with essentials not produced by the roots themselves. Here the carbohydrates are quantitatively the most important, whereas also specific substances have to be transported to the roots. It can be demonstrated that in general the macro-nutrients, mentioned above, regulate the equilibrium between the transpiring photosynthesizing leaf surface and the absorbing root surface. External factors inducing high transpiration (high light intensity, low relative humidity) or reducing water absorption (dry soil, low root temperatures) tend to decrease this ratio, predominantly by either decreasing leaf growth more than root growth or increasing leaf growth less than root growth. Since leaf growth is more sensitive to adverse conditions than photosynthesis, the external conditions, listed above, all induce an accumulation of carbohydrates in the plants, which is favourable not only to the relative rate of root growth but also to various additional features of morphological differentiation. These features frequently have consequences for the equilibrium between transpiring and absorbing surfaces. Some of these are listed in the tables 1-3. Salt addition to the root environment leads to a sudden decrease in transpiration and photosynthesis. Since the plants are not yet adapted this decrease is the same on a leaf area basis as on a plant dry weight basis.