There is an old saying that "the plant makes soil". Fallow and rotations in the past did a great deal to maintain fertility without the use of fertilisers. The shifting cultivators of the early days of farming and in parts of Africa today would leave the soil to restore itself over a long fallow of up to twenty years or so. This restoration of fertility must be due to self-colonised plants (weeds) which return to the soil the nutrients that the sown crops had removed. Prof. Kervran says that daisies settle on lawns lacking in calcium and they " create " the calcium the soil requires. The plant, therefore, in this process of restoring fertility, puts into the soil minerals that it has not taken from it. We think of crops in our own monocultural farming as only taking from the soil, not feeding the soil. Prof. Kervran's experiments on biological mutations give an explanation of this phenomenon.