Sprengel identified that flowers were essentially organs designed to attract insects that aided in pollination. He observed that nectar was an attractant and that the petals had markings that guided insects to the nectar. He also observed dichogamy, both protogyny and protrandry and pointed out that this helped prevent self-pollination. He also noticed self-incompatibility. He classified insects as generalists and specialists and identified the principle of buzz pollination in "Leucojum". He noticed that some flowers were nectarless, especially those that were wind-pollinated. He also observed that some flowers such as orchids attracted insects but did not have nectar but he did not fully understand the nature of the deception. He also recognized nectar theft by certain insects.