412 MINNESOTA STATE HORTICULTURAL SOCIETY. 



been causing such gall-like swellings. But this is not the case, as 

 these insects, the larvse of small flies, have simply utilized the dis- 

 eased condition of the plum for their own use. The bladders, or 

 pockets, (Fig. 2, a) are caused by the presence of a parasitic fungus 

 which attacks the 3'oung plum and, by growing inside its tissues, 

 causes the peculiar growth. It is really strange that until quite 

 recently very little of a definite character was known about the 

 pockets, though they were described as early as 1593 by Casalpin. 

 For a long time many theories were advanced to account for their 

 formations, such as insects, improper fertilization or too abundant 

 inoisture at the time of setting of the fruit. Fuckel discovered the 

 true cause in 1861, and a few years later it was thoroughlj^ studied 

 by De Bary. 



Here in Minnesota the pockets appear soon after flowering, grow 

 rapidly and drop from the trees towards the end of June. First, al- 

 most globular, they soon assume an oblong, oval, twisted or curved 

 shape. They are very variable in size, and some grow to almost two 

 inches in length by an inch in diameter. At first they are smooths 

 resembling the healthy fruit, but differ from it by a yellowish or 

 reddish color. I recollect the time when, as a boy, myself and other 

 youngsters peeped into every tree to find such bladders, as they 

 were considered great delicacies; evidently, a depraved taste based 

 upon ignorance of the cause that made them. When the pockets 

 reach maturity their color gradually changes to gray, produced by 

 fine gray powder dusted over them, and later the^^ turn to dark 

 brown or black. In this condition they soon become hard and drop. 



When we cut through such a pocket we find that the walls are 

 quite thick, and that instead of a stone the cavity is filled more or 

 less with the threads of a fungus. But this disease attacks also the 

 younger branches and leaves, which also become contorted, turn 

 gray and die toward autumn. One of the worst features of this dis' 

 ease lies in the fact that trees once infested are very apt to produce 

 more and more bladders year after year, and that they hardlj' ever 

 recover. Some varieties are less liable to the disease; it is very 

 common upon the wild red plum (Prun us Americana), the dwarf 

 cherry (Cerasus pumila), the wild black cherry ^Cerasus serotina), 

 and upon the choke cherry (Cerasus Virginiana). 



A microscopic investigation will reveal three distinct organisms: 

 mycelium, asci and spores. The former is a colorless bundle of 

 filaments or threads; it is most readily seen inside the ilesh of the 

 pocket. From there the mycelium forces its way towards the sur- 

 face, and bj^ branching repeatedly forms a rather dense network 

 between the epidermal cells and the cuticle, only one cell in depth 

 (Fig. 2, c). The cells in this network are very short, soon start to 

 grow at right angles, and so form small cj'linders standing erect 

 side by side. Before long the cuticle is ruptured and the cylinders 

 appear upon the surface (Fig. 2, d, e). They are the immature asci^ 

 and are filled with granular protoplasm, whicli during growth 

 passes into the free ends and becomes eventually separated by a 

 septum. This separated portion is the true ascus. The protoplasm 

 inside gradually separates into a number of spores, usually eight 



