He stayed thirty years in the Dutch East Indies and did research on plant taxonomy on the islands of Java and Madura.

Immediately he started to collect the plants around him, but to name them unreliable or incomplete treatises had been written, now also outdated and often not readily available.

Thus, he decided to write one himself, with the flora of his immediate surroundings as a start, and this marked a milestone in his life and for Malesian botany.

He scoured the fields and forests of Java, Madura, and the adjacent Kangean Islands, and so collected about 30,000 specimens while making daily trips of thirty to forty kilometres on foot.

[6][7] In 1929 Backer published his contentious book The problem of Krakatao, as seen by a botanist, in which he maintained that not all plant life had been destroyed by the gigantic eruption of the volcano, but that rootstocks and diaspores might have been buried to sprout again.

Only as late as June 1886 the first biologist, Melchior Treub, came to take stock, but grasses had already been observed on the slopes in 1884 by the Dutch geologist Rogier Verbeek (1845–1926).