"Until about the beginning of the present century all the spawn used in America was imported from England or France. Interest was started in its manufacture here by the work of B.M. Duggar and Miss Ferguson, of the United States Bureau of Plant Industry. They gathered the spores from different mushrooms and produced the mycelium in test tubes filled with horse manure. This was afterwards transferred to the manure bricks and was put on the market as "Pure Culture Spawn." By this method the varieties were isolated and could be kept pure. Since that time mushroom culture has had a great boom."