 He had become interested in phytogeography and plant ecology, undertaking expeditions to the West Indies and Venezuela in 1882–1883.In 1886, he stayed with Fritz Müller in Brazil, and in 1889–1890 in Ceylon, the Malaya and Botanical Garden in Buitenzorg (Bogor, Java), concentrating on mangroves, epiphytes and littoral vegetation.This resulted in his account of the Rhizophoraceae in Engler & Prantl's "Natürliche Pflanzenfamilien".