Foxglove seed surface (Digitalis purpurea), coloured scanning electron micrograph (SEM). This image shows the seed coat (or testa) of a foxglove seed (Digitalis purpurea). The testa has an irregular honeycomb-like structure. The purpose of the seed coat structure is to enhance seed germination. The seed coat traps small particles of dust and soil so that when the seed falls to the ground it is anchored and can germinate easily. The testa is mechanically protective and limits entry of solutes into the seed. Foxglove plants are found growing wild in Europe and the USA in woodland and on dry heaths. The leaves are the source of the drug digitalin (a heart drug), for slowing the pulse rate in treatment of heart disease. The flowers are produced on a tall spike, are tubular, and vary in colour with species. Magnification: x185 when shortest axis printed at 25 millimetres.