During some trips to several points on the Dutch and French coasts barnacles were collected in order to get an impression of the algal microvegetation perforating into the shells and growing on them. The barnacles were dried or conserved in formaldehyd-solution; they were decalcified in diaphanol. By treating slides with chloriodide of zinc the chlorophyceae could be distinguished from the remaining algae by their cell-walls and starch-grains stained violet and blue.