The perfect stage of a species of Leptographium isolated from lesions on western white pine affected with pole blight has been described as Europhium trinacriforme and a method has been outlined for obtaining perithecia in culture. Studies on the sexuality of the fungus have revealed it to be heterothallic with two compatibility types. Cross-fertilization experiments revealed the presence of isolates which acted as either males, females or hermaphrodites. E. trinacriforme was isolated from 11 per cent of the lesions on western white pine affected with pole blight in the Interior region of British Columbia and from 84 per cent of the lesions on affected trees in the Coast region. The fungus was the only pathogenic organism isolated more than twice from lesions and it was shown to be capable of producing lesions similar in several respects to pole blight lesions. However, further data from isolation, inoculation, histological and radial growth studies have shown that pole blight lesions were not caused directly by E. trinacriforme. It is most likely that the fungus gained entrance to lesions already formed and occasionally extended them. / Science, Faculty of / Botany, Department of / Graduate