The plum in common with other stone-fruits often suffers from an excessive flow of gum, for which trouble the name gummosis[168] is now generally applied. The disease is to be found wherever plums are grown but it is much more destructive on the Pacific than on the Atlantic seaboard. So far as is now known gummosis is secondary to injuries caused by fungi, bacteria, insects, frost, sunscald, and mechanical agencies. The disease is least common in species and varieties having hard wood; on trees on soils favoring the maturity of wood; under conditions where sun and frost are not injurious; and, obviously, in orchards where by good care the primary causes of gumming are kept out. Stewart[169] has recorded an interesting case of gum-pockets in the fruit, but could assign no cause. Mechanical injuries from the sun, frost and hail are troubles with which nearly all plum-growers must contend at one time or another. In this region the Reine Claude and Triflora plums suffer much from sunscald but none are wholly immune, though Lombard is possibly most so. These injuries from the elements of weather are often mistaken for diseases, and are so often followed by fungal parasites and insects as to make it difficult to distinguish the primary from the secondary trouble. Low-heading of the trees is the best preventive of these trunk injuries. Plums are somewhat subject to attacks of the well-known peach scab[170] (_Cladosporium carpophilum_ Thumen). The scab appears in numerous, small, sooty, circular spots of brownish color, often confined to one side of a fruit but in other cases distributed over the whole surface. None of the cultivated species are free from the disease but the Munsoniana, and Hortulana varieties are most susceptible to it. Pear blight,[171] (_Bacillus amylovorus_ (Burrill) DeToni) commonly thought of as a disease of the pear and apple has been found on various plums, and the yellows of the peach, cause unknown, is often quite destructive to Triflora plums. According to Smith the peach rosette,[172] cause unknown, attacks both wild and cultivated plums in the South and is quickly fatal. The disease was prevalent on the wild Angustifolias, on two varieties of Triflora, Kelsey and Botan, but the observer had not seen rosette on varieties of Domestica.