Sprengel began his botanical explorations in 1787. That summer he noticed that the wood cranesbill ("Geranium sylvaticum") had soft hairs on the lower part of the petals. He decided that they played a role and came up with the idea that they protected the nectar from rain in the same way that eyebrows and eyelashes prevented sweat from entering the eye. He collaborated with Willdenow and described "Silene chlorantha" (Willd.) Ehrh. (Caryophyllaceae) which is extremely rare in Berlin district. It took six years before Sprengel actually published his works. The book was based on the studies of 461 plants and included 25 copperplate engravings based on his own drawings.