to 1977, during which time 49 were sold. Ulmus thomasii was crossed experimentally with Japanese elm (U. davidiana var. japonica) at the Arnold Arboretum in Massachusetts, but no clones were released to commerce. Seedlings arising from crossings with Siberian elm (U. pumila) at the Lake States Forestry Experimental Station in the 1950s all perished, a classic case of hybrid lethality. Notable trees The US National Champion, measuring high in 1989, grows in Cass County, Michigan. Uses The wood of the rock elm is the hardest and heaviest of all elms, and where forest-grown remains comparatively free of knots and other defects. It is also very strong and takes a high polish, and consequently was once in great demand in America and Europe for a wide range of uses, notably boatbuilding, furniture, agricultural tools, and musical instruments. Much of the timber's strength is derived from the tight grain arising from the tree's very slow rate of growth, the trunk typically increasing in diameter by less than a year. Over 250 annual growth rings were once counted in a log square being sawn for gunwales in an English boatyard, while a tree once grown at Kew Gardens, London, attained a height of only in 50 years. Accessions North America Arnold Arboretum, Massachusetts, US. Acc. no. 444-88. Brenton Arboretum, Dallas Center, Iowa, US. No acc. details available. Dominion Arboretum, Ottawa, Canada. No acc. details. Morton Arboretum, Illinois, US. Acc. no. 178-84, wild collected from Reedsville, Wisconsin; 843-2005 (Kelleys Island, Erie County, Ohio); 122-2006 (Dixon County, Nebraska). Nebraska Statewide Arboretum, US. No details available. Europe Grange Farm Arboretum, Lincolnshire, UK. Acc. no. 706. National Botanic Garden of Belgium, Meise, Belgium. Acc. no. 19800105. National Botanic Gardens, Ireland, Glasnevin, Ireland. Location: A3 (155) Sir Harold Hillier Gardens, Hampshire, UK. Acc. no. 2008.0419, wild collected in Ontario, Canada, by Kristl Walek Wakehurst Place Garden Wakehurst Place, UK. Acc. no. 1968-48603. References External links Arnold Arboretum specimen, 1960 Labeled U. racemosa, RBGE specimen from Späth nursery, 1902 Labeled U. racemosa, RBGE specimen from Späth nursery, 1902 Labeled U. racemosa, RBGE specimen from Späth nursery, 1902 thomasii Trees of the Northeastern United States Trees of the Great Lakes region (North America) Trees of the Plains-Midwest (United States) Trees of Canada Trees of the North-Central United States Trees of Ontario Trees of Quebec Trees of the Southeastern United States Ulmus articles with images Elm species and varieties