It is easy to assure oneself that the spermogones and cluster-cups proceed from the mycelium of the sporidia which had been sown. During several days the length and number of the peridia of the _Æcidium_ continue to increase. One month after sowing, brownish or blackish points make their appearance upon the whitish spots, around, or intermingled with the cluster-cups. These increase rapidly in number and magnitude. Examined by the microscope, they present the ordinary fructification of _Uromyces_, mingled with stylospores. Thus the mycelium of the cluster-cups engenders at the end of its vegetation fruits equal in all points to those from whence they are in the first instance derived. The stylospores of the cluster-cups possess the irregular, globular form and structure of their congeners. They are filled with orange granular matter, and provided with a colourless, finely-punctated epispore. When these stylospores are sown on the moistened epidermis of a favourable plant, the germ-tube at first creeps along the surface, but as soon as its extremities find a stomate, it enters it and elongates itself in the air-cavity below the orifice, receives the contents of the original stylospore and exposed portion of its tube, then separates itself from those parts, which become dispersed. The active part increases and ramifies, and produces a mycelium which spreads through the intercellular passages of the parenchyma. At the end of from six to eight days, the whitish spots appear on the surface of the fostering plant, and indicate that the fructification of the parasite is about to commence. The epidermis is elevated and broken, and little brown pustules appear through the openings. These are the _stylospores_ of _Uredo_, which are produced in immense quantities, and soon cover the pustules with a deep brown dust. Later, the formation of the stylospores is arrested, and the true germinating spores appear in the same pustules.