IN the same way as a certain number of mineral substances and chemical elements are necessary to the life of green plants, so fungi are unable to live without most of the same substances. Analysis shows that phosphorus, potassium and nitrogen are required, but quite tiny quantities of other substances also are necessary for growth. The fact that iron is concerned in the formation of the green colouring matter of flowering plants led to the assumption that no iron is necessary in fungi from which the green-colouring matter (chlorophyll) is absent. But when tests were made, it was found that

small quantities of iron are essential, and that iron could also act as a growth stimulant. The chief food of fungi is provided by the material forming the living or dead bodies of plants and animals.

This property of converting atmospheric nitrogen into soluble substances that can diffuse through a cell-wall is one of the most important of biological processes, and amongst the ‘nitrogen-fixers,’ as they are called, particular mention must be made of the nodule organism which occurs in the nodular swellings on the roots of plants of the pea and clover family. When the seed of a clover plant germinates, the root is at once attacked close to the tip by nitrogen-fixing bacteria

which enter the root hairs, multiply rapidly and form shiny-cords and make pockets in the root. About the time the plant flowers, the majority of the bacteria are absorbed by it, but a few are returned to the soil and provide for the re-infection of the next generation of plants. The ‘fixation ‘of atmospheric nitrogen by the nitrogen fixing bacteria of the soil is of great importance to agriculture and indeed to the fertility of the whole earth.

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