In 1905 another visit was paid to Krakatau, in which Th. Valeton, M. Golenkin and other botanists took part. The results of this expedition have not been published.

During my residence at Buitenzorg I made application, in company with C. A. Backer, the author of a comprehensive “Flora of Batavia” which is now in the press, to Professor Treub to organise another expedition for the investigation of the Krakatau flora. As the result of his kind co-operation the authorities placed at our disposal a small coasting steamer which was then on the point of visiting certain places on the coast of the Sunda Strait to relieve the lighthouse keepers. The excursion was to last four days and the departure was fixed for April 24th. Unfortunately Professor Treub was prevented by illness from accompanying us, but we were joined by two botanists who happened to be studying in the Buitenzorg botanic garden, Dr A. A. Pulle from Holland and Prof. D. H. Campbell of California.

The plants collected by C. A. Backer and Dr A. A. Pulle in the course of our Krakatau excursion, on the island and at different localities on the coasts, were determined by the former, who was kind enough to undertake the revision and to some extent the identification of the vascular plants collected by myself.