This paper presents recent information on the biology of Agrobacterium tumefaciens, and outlines techniques for isolating and studying the bacterium. Data are presented indicating that A. tumefaciens is a soil inhabitant. The organism was isolated in 18 of 28 California soils, including soils not known to support host plants, and appears to be a rhizosphere organism. In vitro experiments showed that the bacterial cells aggregated around roots of various plants.

A. tumefaciens and A. radiobacter were studied for serological and physiological differences. Although no physiological differences were detected, most A. tumefaciens strains differed serologically from A. radiobacter in possessing an antigen which formed a precipitin line near the antigen well in gel-diffusion tests. The last part of the paper discusses how the disease is contracted and presents techniques for reducing loss from crown gall.