A rooting runner of a blackberry, Rubus fruticosus. The picture shows the tip of a runner of a Himalayan Giant blackberry that has developed roots and shoots (red). A runner is a fast growing stem produced in late summer that grows downwards towards the soil, showing positive geotropism. This is how blackberries spread by vegetative reproduction. On contact with soil, the stem (picture top, with small thorns) first produces roots (white) that anchor the tip.This is followed by the development of shoots (red). The process results in the formation of a new plant, which may be a metre or more distant from the original. In horticulture, such plants can be separated from the parent and planted elsewhere. In nature, the result is an ever-expanding colony. In a garden, the behaviour is called invasive.