The kingdom Oomycota includes a number of fungus-like groups such as the downy mildews and white rusts. They produce similar threads called hyphae and secrete enzymes to digest their food before absorbing the released nutrients. They differ from fungi in that their cell walls are made of cellulose rather than chitin. Phytopthera is responsible for blight in potatoes and Pythium causes the damping-off of seedlings.