In the winter and early spring of 1916 Mrs. Anna Weber-van Bosse at her hospitable residence near Eerbeek initiated me in the study of Freshwater Algae. For several years after that date in numerous trips all over this country I collected and studied some thousands of samples from all kinds of freshwater ponds and lakes, canals and streams. The Desmids soon drew my special attention, when an unexpectedly rich and varied Desmid flora was found in certain fens and ponds in the diluvial and moor districts of our country.