What type of plants did Darwin study in his 1875 book?

What type of plants did Darwin study in his 1875 book? He studied insectivorous plants.

Darwin's book Insectivorous Plants, published on 2 July 1875, examined plants that capture and digest animal prey. Modern botanical writing more often calls them carnivorous plants, but “insectivorous plants” was the historical term used in the book's title. Darwin focused especially on how these plants obtain nutrients in environments where the soil is poor in nitrogen.

His experiments included the common sundew, Drosera rotundifolia, whose sticky leaves trap small insects. He tested how the plants responded to touch, meat and other substances, and investigated their ability to secrete digestive fluids and absorb nutrients. He also compared different trapping mechanisms, including sticky surfaces, snap-like movements and bladder traps.

The book connected plant physiology with evolution. Darwin argued that sensitivity, digestion and prey capture were adaptations shaped by natural selection. He was particularly struck that a plant could produce a fluid resembling an animal digestive secretion. A common mix-up is Orchids: Darwin wrote an important earlier book about orchid pollination, but that was a separate 1862 work. Insectivorous Plants was a detailed study of predatory plant biology.