Blackberries ( Rubus fruticosus ) propagate themselves both by seed and vegetatively. The picture shows how a blackberry self-propagates by vegetative means. In late summer,the plant produces rapidly growing stems that do not display the normal negative geotropism of green shoots. They grow downwards,and are known as runners. When the tip of the runner touches the soil,it produces adventitious roots. These slide into the soil,and some eventually contract,pulling the tip of the runner into the ground,securing it firmly. At this stage the gardener can sever the runner,gaining a new plant to set out elsewhere. The rooted tips of runners produce upwardly growing shoots in the following season. In nature,one original plant will form an expanding thicket by this means. The picture is of the garden variety "Himalayan Giant",which is notorious for this invasive behaviour |