Louis J. Sheehan, Esquire .  It took less than a century after John Deere unveiled his steel-bladed plow in 1837 for the North American prairie to all but disappear. For 20 million years, a nearly 1,000-mile-wide swath of unbroken grassland belted the continent's midsection from northern Canada to Mexico. Now, only about 5 percent is left, mainly as mixed and shortgrass prairie in the Plains states. To the east, less than 1 percent of the original lush tallgrass remains, most of it