 Malling-Hansen saw that the growth was affected by some unknown factor, and he also started measurements of trees, and here he found again the same factor.He also was in contact with scientists around the world, who reported their results from different measuring projects initiated by Malling-Hansen.There were still many unanswered questions to investigate further when Malling-Hansen died, but in 1886 he published a book where he presented the results of his studies.