SUMMARYOver 120 randomly selected strains belonging to 16 genera and to more than 80 species of Desmids were brought into uni‐algal culture and subjected to conditions provoking conjugation. Only 3 isolates – all homothallic – exhibited sexual reproduction:Closterium limneticumLemn.,Cl. moniliferumBory ex Ralfs, andMicrasterias papilliferaBréb. OfCl. limneticumno zygospores had previously been known. The, generally speaking, poor result of the experiment supports the theory that it is a lack of sexual potential rather than ecological factors which is responsible for the rare incidence of sexual reproduction in Desmids under natural cond