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tamarisk was beginning to spread along the rivers. (1965), it has now spread to nearly a million acres States. According to Robinson in the western United There is still confusion as to the proper orlgln of tamarisk from the Old World. Originally it was thought to be the French tamarisk (!. gallica), a native of the Mediterranean region, but recent studies have shown that the French tamarisk has been naturalized only in the Texas and Gulf of Mexico area (Horton, 1964). Our western tamarisk has been called !. penta~dra, but more recently even this name has become questionable (Baum, 1966). It appears to be similar to a species growing in Asia from China to Mongolia and Turkistan. If it is this species, rapid spread of tamarisk in colder parts of the United States is to be expected and experience in the Rocky Mountain area is showing that this is true, even in the cold Northern Plains. The question is often asked as to why tamarisk is such an aggressive invader in flood-plain lands. The answer lies in the fact that the seeds are very abundantly produced and will germinate readiLY in wet conditions (Horton, Mounts, and Kraft, 1960). The seedlings will survive, however, only where the soils are moist for several weeks during the summer period. Thus, any areas that have been flooded, or where the soils are kept continuously moist, such as along the edges of reser- voirs and streams, are subject to rapid invasion of tamarisk. There are many cases on record where reservoir deltas, near an area with mature tamarisk for a source of seed, have become completely covered with tamarisk when the water level in the reservoir dropped during the summer period. Tamarisk now grows almost throughout the western United States. It often occurs in dense stands on the flood plains of the major rivers, as well as growing as a fringe along the rivers and streams in the mountains. In intermittent stream channels and around springs, seeps, and stock tanks, the species occurs as isolated specimens. In fact, there is very little moist area in the Southwest now where you cannot find tamarisk either as individual plants or as colonies. On flood plains, where tamarisk reaches its greatest abundance and vigor, the species can be controlled if the savings of water or the need for the land for other purposes make the cost of clearing feasi- ble. Mature stands of tamarisk are best removed by mechanical means, usually either by rootplowing or bulldozing. Mechanical methods are most successful if the work is done when the weather is warm and the soil is dry. Otherwise, there is a tendency for tamarisk stems that are buried in moist soil to root and form new plants. Mature tamarisk plants will not succumb to fire, even through stands will burn readily under certain weather conditions. The stumps sprout so vigorously that a stand of tamarisk returns quickly. 2