The influence of plant cytology on the construction of cytological practices with animal cells is explored here. This short essay aims at a dialogue with Hans-Jörg Rheinberger's proposal about the intersections between objects and instruments and about how to look at slide "preparations." I select microscopic preparations of chromosomes to analyse the practices and meaning of polyploidy as an historical object. The study of the practices of Swedish geneticist Albert Levan by the late 1940s and early 1950s suggests that polyploidy filled the gap between plants and animals, while at the same time accounted for differences between the two.