When fruit-tree flowers are fully expanded, or even one half of them have opened, it is not easy to prevent self-pollination. It is far safest to begin the work when the first flowers are nearly expanded. The petals are clippped off with small scissors, followed by carefully clipping off the anthers. At once, after emasculation, the flower or flowers left in a cluster are covered with a paper or muslin bag. The writer's experience favors the use of muslin bags, as they can most rapidly be gathered and pinned to hold the bag in place and to exclude insects. In case high winds and rains occur the thin muslin sacks are not torn or displaced, as often happens with the paper sacks, and they are not so much swayed by the winds, which with the paper often injure the delicate pistils and ovary. The novice who knows the parts of the flower can do this simple work as well as the expert, and those who do not know the parts will make no mistake if a minute's study is given to Fig. 10, showing an enlarged flower of the cherry, The floral part, marked (cor), is clipped off before opening fully and the stamens around the centre, marked (S), are clipped off, taking care that the anthers do not lodge in the emasculated flower. With the fruit blossoms that grow in clusters, all should be clipped except one or two of the strongest. In Nature it is not common for more than one fruit to set in a cluster. With monoecious and dioecious flowers (34. Monoecious and Dioecious Flowers) and pistillate flowers (35. Perfect and Imperfect Flowers) we have no stamens to take from the flowers supplied alone with pistils. But they should be covered before fully opening to exclude foreign pollen.