Varieties of American grapes show most remarkable differences in the degree of self-fertility. Many sorts fruit perfectly without cross-pollination. Others set no fruit whatsoever if cross-pollination is not provided for. Most varieties, however, are found in groups between the two extremes, neither self-fertile nor self-sterile. Figure 51 shows staminate and perfect clusters on one vine. Some varieties show no variation in the degree of self-sterility or self-fertility; others behave differently in regard to these characters under different environment. Now and then the widest variations are to be found in a variety in respect to self-fertility. [Illustration: FIG. 51. Staminate and perfect clusters on one vine; _right_, staminate; _left_, perfect.] Following the lead of Beach at the New York Agricultural Experiment Station, several workers have made careful studies of the self-fertility of the grape, and now the cultivated varieties of native grapes are divided into four groups in accordance with the degree of self-fertility. Class I includes self-fertile varieties having perfect or nearly perfect clusters; Class II includes self-fertile varieties having clusters loose but marketable; Class III includes varieties which are so imperfectly self-fertile that the clusters are generally too loose to be marketable; Class IV includes self-sterile varieties. The following is a list of commonly cultivated grapes classified according to the divisions just given: CLASSIFICATION OF GRAPES ACCORDING TO SELF-FERTILITY CLASS I. Clusters perfect or varying from perfect to somewhat loose. Berckmans Bertha Cottage Croton Delaware Diana Etta Janesville Lady Washington Lutie Moore Early Poughkeepsie Pocklington Prentiss Rochester Senasqua Winchell CLASS II. Clusters marketable; moderately compact or loose. Agawam Brilliant Brown Catawba Champion Chautauqua Clinton Colerain Concord Dutchess Early Victor Elvira Empire State Fern Munson Hartford Iona Isabella Isabella Seedling Jefferson Jessica Lady Mills Missouri Riesling Perkins Rommel Triumph Ulster CLASS III. Clusters unmarketable. Brighton Canada Dracut Amber Eumelan Geneva Hayes Lindley Noah Northern Muscadine Vergennes CLASS IV. Self-sterile. No fruit develops on covered clusters. America Aminia Barry Black Eagle Clevener Creveling Eldorado Faith (?) Gaertner Grein Golden Hercules Jewel Massasoit Maxatawney (?) Merrimac Montefiore Requa Salem Wyoming