In the six decades since the first edition of this book was prepared, nematodes have become of major importance in plant pathology. It used to be stated that plant pests, insects, and diseases, took a toll of one-tenth of all our crops. Now we believe that nematodes alone may cause a 10 % crop loss, and some place the figure as high as 25 %. The monetary loss is not easy to figure. Guesses range from $500,000 to $8 billion a year in the U. S. Nematodes may be as damaging in home gardens as on farms.