Tumor induction in germ-free rats fed bracken (Pteridium aquilinum).

This study indicated that there was no significant difference in the incidence of intestinal tumors between germ-free and conventional rats fed a diet containing bracken, suggesting that gut microflora did not play a definite role in bracken tumorigenesis. However, bracken induced exclusively sarcoma but no adenocarcinoma in germ-free rats, whereas it induced predominantly adenocarcinoma in conventional rats.