The principle of bionic is, however,by no means new. The designs of many machine , both ancient and modern, have been based on natural forms. One example is the propeller. The seeds of certain trees have wings ,which are slightly twisted. When these seeds fall from the tree , their wings make them spin round , so that they can fly quite long distances if the wind is favourable. Observation of such seeds suggested the idea of making machines with spiral blades of this kind. When the blades were rotated rapidly, the machines could fly , or move through water. So the propeller and the helicopter roter were invented. Another early example of bionics was the invention of flying machines with wings like those of birds or bats