The six clones which comprise this series vary considerably in their level of resistance to Dutch elm disease, and none is immune, but some evidence suggests that at least one of the six clones may have a fairly high degree of DED-resistance. It is claimed, controversially, by ERI that fewer than 180 American Liberty elm trees have been known to succumb to DED since the planting began in the early 1980s. This figure is surprising in the light of Townsend & Douglass's work, which found that the Liberty elms exhibited only an 18% survival rate four years after inoculation, compared with 96% for both 'Valley Forge' and 'Princeton', and 100% for the Japanese elm clone 'Prospector'.