Several interesting and sometimes destructive diseases of plums are caused by various species of the fungal genus Exoascus.[158] The most common of these, and the most striking and destructive, is plum-pockets (_Exoascus pruni_ Fuckel), which causes prominent deformities of the fruit. These give the disease the common name or less frequently “bladders” and “curl.” The fungus attacks the developing fruits at an early stage of their growth and causes the production of a spongy mass in the fleshy tissue which greatly enlarges and distorts the plum. The stone in a diseased plum is but rudimentary or very often not at all developed. Less prominently but quite as frequently, the leaves are attacked, showing as they unfold more or less red or yellow with a very decided curling and arching of the leaf-blade. The disease usually spreads from the leaves to the shoots, the infected shoots with their rosettes of mal-formed leaves giving the tree a most unsightly appearance. Prevention at present consists of removing the diseased parts and spraying with bordeaux mixture when the buds begin to swell. Munsoniana and Hortulana plums seem to be most susceptible to this disease. Atkinson[159] has described several species of Exoascus on the different species of wild plums, some of which are liable to be found on the cultivated varieties of the native plums. They are all very similar to _Exoascus pruni_, differing chiefly, in the eyes of the layman, in forming smaller pockets. Sturgis[160] records an attack of one of the leaf-curl fungi, distinct from the plum-pockets fungus, on varieties of Triflora in Connecticut, which seemed to him to be of scientific and economic importance. The leaves of the different species of cultivated plums are attacked by several fungi which produce diseased spots on the foliage, which for most part drop out, causing a shot-hole effect. These diseases pass under such descriptive names as “shot-hole fungus,” “leaf-spot,” and “leaf-blight.” The fungus probably responsible for most of this trouble is best known as the shot-hole fungus[161] (_Cylindrosporium padi_ Karsten). The Domestica and Triflora varieties are very susceptible to this fungus, which, on the foliage of the first, causes spots for most part, while on the latter the spots on the leaves are nearly always followed by holes. Varieties of the native species, especially those of Americana and Nigra, are relatively free from this disease. Another of these shot-hole fungi is _Cercospora circumscissa_ Saccardo[162], much less common than the former, but still to be considered and especially on the foliage of Americana. All of these diseases of the foliage are prevented to some degree by the proper use of bordeaux mixture, which, on the Triflora plums at least, must be used with great care to avoid injury. Cultivation has a salutary effect as it destroys the diseased leaves which harbor the fungi.