He became an instructor at the University of Michigan in 1923 and came to the University of Pennsylvania as a National Research Fellow in 1924 and became a professor of protoplasmatology and plant geography in 1925.
32.
Wahlenberg made his main work in the field of plant geography and published, among other things the " Flora lapponica " ( 1812 ) and other works on the plant world of northernmost Sweden.
33.
He published numerous treatises on botanical subjects,---discussing questions of system, organography, physiology, plant geography, and paleontology---in various periodicals, chiefly in the " Giornale botanico Italiano " ( 1844-), which he founded.
34.
He has written academic papers and books on chalk grassland, on the vegetation and archaeology of Thailand ( and on the rest of southeast Asia ), on ecology and biogeography ( e . g . his textbook'Historical Plant Geography'), on fire ecology on lichens and mosses, on tropical rain forest and on the construction of environmental knowledge.
