Book excerpt: During the war years, 1944 to 1946, the second author (R.E.) had an unusual opportunity to become familiar with almost all the known thermophilic fungi. He was serving as Microbiologist, with Dr. Paul J. Allen, in the Guayule Rubber Extraction Research Unit of the United States Department of Agriculture at Salinas, California. The Microbiology Laboratory was engaged in a detailed investigation of guayule retting, a process in which the rubber-producing shrub, Parthenium argentatum, wass subjected to microbial action in order to yield a rubber of improved quality.