This paper is based on correspondence between M.A. Lieftinck and D.C. Geijskes (archives Museum Naturalis, Leiden). Geijskes, then still at highschool, found Aeshna viridis near Berlicum, province of Noord-Brabant in 1926, and observed that this species was confined to broads with Stratiotes vegetation. Lieftinck confirmed the identification, and explained the strict correlation of A. viridis with Stratiotes. Geijskes also described his observations on oviposition in Lestes viridis, apparently not commonly known at the time. The observations on Lestes viridis were published in Geijskes (1928), those on Aeshna viridis in Geijskes (1931), but the style of the original letters adds significantly to the understanding of the state of knowledge of odonatology in The Netherlands in the 1920s.