Phragmidium
(from the Greek phragmos, a fence; in allusion to the partitions between the numerous cells in each spore). A small genus of Fungi, belonging to the group popularly known as Brands, or in science as Uredineae. The species best known to gardeners are those that cause the Raspberry Brand (P. Rubi-Idaei, Pers., or P. gracile, Grev.) on wild and on garden Raspberries, and Rose Brand (P. mucronatum) on Rose-leaves. In all the species of Phragmidium, the Fungus appears on the green parts, especially on the leaves, in the form of small spots, usually very numerous, on the lower surface. The leaf is, in some plants (e.g., Bramble), discoloured around the spots; in others (e.g., Raspberry), it is not discoloured. The Fungus is, at first, yellow, and the spots are seen, with the aid of the microscope, to be made up of masses of globular, or angular, yellow cells or spores. In this stage, the species of Phragmidium used to be referred to the genus Lecythea. As the Fungus matures, the spots become dark brown or black, and the spores then present are much larger than those produced in the previous stage. Each consists of a single row of cells, from three to ten in number. They are very dark brown when mature, and are supported on slender footstalks. The species on Raspberry has eight to ten cells in the spore. The Fungus, as observed on the leaves, is reproducing the species, and the spots are masses of spores formed at certain places; but the more important part is the mycelium, which grows among, and feeds on, the tissues of the host-plant. The Brands of this genus are, as a rule, not very hurtful to cultivation, though both the above, viz., Rose Brand (P. subcorticium, Schr., or P. mucronatum, Fr., with six to eight-celled spores) on Roses, and P. Rubi-Idaei on Raspberry, are common. The only remedy is to remove and to destroy all the diseased leaves, by burning or by digging into the soil.