Elms for the Future

Abstract

An American city without elm trees would be something like a baseball game without hot dogs. The tall, stately trees have shaded many an American home for generations, made cool, green tunnels of our streets and diverted the icy blasts of winter in towns from coast to coast. But the elms as we know them are doomed. An incurable fungus-Dutch Elm Disease-is gradually spreading through the United States, choking off the life of tree after tree, leaving only peeling stumps in its wake. Though the disease first appeared in this country in 1930, brought in on elm logs from the Netherlands, it has done most of its damage in the last 10 years. Efforts to contain it have been sporadic, ranging from mobilization of entire towns in some places to shouldershrugging acceptance of the pestilence in others. Even those who know most about it admit they really understand very little-just why some trees seem to be immune, exactly how the disease attacks a tree are still mostly mystery. There are two ways to deal with the disease, the botanists say. Present stands of American elm can be largely protected by DDT spraying to kill the beetles that transmit the disease or new, disease-resistant varieties of elm can be developed. This latter effort has occupied the minds of a good many plant biologists for more than three decades without, producing a really satisfactory solution. There are disease-resistant elms now available, but they are not as desirable shade trees as the native American elm. All efforts to cross American elms with resistant species such as Siberian elms, combining the best features of both, have failed. The first successful such cross may be in the offing, however, if the theories of scientists at the Department of Agriculture's Plant Industry Station in Beltsville, Md., prove out. American elms have twice the number of chromosomes as any other species. Concluding that the failure of earlier hybrids was due to that fact the scientists have prepared a tailor-made mate by doubling the chromosome count in Siberian elm seedlings. They did it by daubing each plant, as soon as a growing bud appeared, with a drug called colchicine that is also used in the treatment of gout. Colchicine, for some reason that is not yet clear, stops the cells in the bud from dividing, but not until the chromosomes in each cell have replicated, creating an extra set of chromosomes. As each seedling grew, the scientists carefully pinched off every unaltered leaf and stem, permitting only the branches with doubled chromosomes to grow. Even then, they did not get entirely altered plants. But, by patient selection and rooting USDA /AFA