Putting a piece of the affected leaf between two pieces of pith so as to hold it firmly, with a little care thin vertical sections of the leaf, including one of the cups, may be made, and mounted, either in water or glycerine, removing the air with alcohol. We find that the leaf is thickened at this point owing to a diseased growth of the cells of the leaf, induced by the action of the fungus. The mass of spores (Fig. 47, _G_) is surrounded by a closely woven mass of filaments, forming a nearly globular cavity. Occupying the bottom of the cup are closely set, upright filaments, each bearing a row of spores, arranged like those of the white rusts, but so closely crowded as to be flattened at the sides. The outer rows have thickened walls, and are grown together so as to form the wall of the cup. The spores are filled with granular protoplasm, in which are numerous drops of orange-yellow oil, to which is principally due their color. As the spores grow, they finally break the overlying epidermis, and then become rounded as the pressure from the sides is relieved. They germinate within a few hours if placed in water, sending out a tube, into which pass the contents of the spore (Fig. 47, _I_). One of the most noticeable of the rusts is the cedar rust (_Gymnosporangium_), forming the growths known as "cedar apples," often met with on the red cedar. These are rounded masses, sometimes as large as a walnut, growing upon the small twigs of the cedar (Fig. 47, _A_). This is a morbid growth of the same nature as those produced by the white rusts and smuts. If one of these cedar apples is examined in the late autumn or winter, it will be found to have the surface dotted with little elevations covered by the epidermis, and on removing this we find masses of forming spores. These rupture the epidermis early in the spring, and appear then as little spikes of a rusty red color. If they are kept wet for a few hours, they enlarge rapidly by the absorption of water, and may reach a length of four or five centimetres, becoming gelatinous in consistence, and sometimes almost entirely hiding the surface of the "apple." In this stage the fungus is extremely conspicuous, and may frequently be met with after rainy weather in the spring. This orange jelly, as shown by the microscope, is made up of elongated two-celled spores (teleuto spores), attached to long gelatinous stalks (Fig. 47, _B_). They are thick-walled, and the contents resemble those of the cluster-cup spores described above.