Translations:Manfred Klett: Von der Agrartechnologie zur Landbaukunst/1333/en

The entire foliage, the four-sided, hollow-stemmed stalk, and the flower are all covered with stinging hairs. These are single-celled outgrowths of the epidermis, reinforced at the base by lime deposits. They carry at the tip a silicified head that breaks off at a touch. The stinging hair pierces the skin like a hypodermic needle and releases a toxic cell-sap that causes the burning — the urticin. This contains among other things substances (histamine, serotonin, acetylcholine) that normally occur only in human beings and animals. In the stinging hairs a physiological process dies into the periphery of the plant — precisely the character of what happens in the blossom. One can therefore say with full justification: not only have the stinging nettle's flowers been drawn down into the foliage, but its aerial shoot is clothed from earliest youth with stinging hairs in a kind of blossoming process.