P. Krook collected plants for Dr Arnold Penther* while on a journey from Port Elizabeth through the Transkei and Natal to the Orange Free State, during January to March 1895. He travelled via King William's Town, Komga, Ntsizwa Mountain (south-east of Kokstad), the Mzimkhulu River, Mkomazi River, Mgeni River, Table Mountain (east of Pietermaritzburg), Estcourt, Harrismith, and the Vaal River. His collection included a few fungi from the Cape, East Griqualand and Harrismith. Penther's plants, including those collected by Krook, were described by various authors in "Plantae Pentherianae", in Annalen der Naturhistorischen Museum, Wien (1900, 1903, 1905, 1910). P. Henning described the fungi (1900), including a new species that he named Puccinia krookii after its collector. A. Zahlbruckner described the flowering plants, naming Chlorophytum krookianum and Lobelia krookii (both since renamed).