DISEASES OF PLANTS. 459 



tion of investigations reported upon in the Annual Report of the station 

 for 1899 (E. S. R., 11, p. 858). The previous publications relating to 

 this disease are briefly reviewed and the geographical distribution in 

 the United States outlined. The various field experiments that have 

 been conducted by the author are reviewed at considerable length, 

 together with his inoculation experiments. The investigations of the 

 author seem to indicate the parasitic nature of the disease and its ready 

 transmission in the soil or by means of inoculation experiments. 



The crown gall, in the author's observations, has been noted upon the 

 peach, apricot, almond, prune, plum, apple, pear, English walnut, and 

 grape, and it is reported by others to occur on the raspberry, black- 

 berry, cherry, poplar, and chestnut. 



The crown gall, according to the author, is annual in its period of 

 growth, beginning in the spring and maturing in the fall. However, 

 in Arizona galls sometimes develop late in the summer and continue 

 their growth throughout the winter when the normal tissues of the tree 

 ave dormant. At first appearance the galls appear as a clear, white, 

 translucent mass of soft, succulent tissue, a millimeter or less in diame- 

 ter and nearly or quite spherical. It is most frequently attached to the 

 host by a narrow neck i to i of the body of the gall. When grown 

 above ground or in water cultures, so as to have access to light, the 

 galls change to a light green from the development of chlorophyll in 

 their outer cells. At first the gall has a rather uniform outer surface, 

 which becomes warty after a time from unequal growth. The white 

 appearance of the gall is lost early in its life and the outgrowth becomes 

 a reddish brown. Any portion of the gall which has changed color has 

 lost the power of further growth. When "the galls decay, as is usually 

 the case at the end of the season's growth, it leaves an open wound 

 through the bark which extends some distance into the wood. The fol- 

 lowing spring a more or less interrupted circle of gall tissue forms 

 around the wound caused by the gall of the previous year. The galls 

 become larger and deeper each succeeding year until finally the stem 

 becomes so weakened that the tree breaks off. 



The cause of the crown gall, in the author's estimation, is due to a 

 specific organism belonging to the slime molds to which the name Den- 

 (iropliagua globosus is given. The various stages of the parasite are 

 described at considerable length and a number of successful inocula- 

 tion experiments, in which sclerotia were used, are described. The 

 effect of the parasite on its host is noted and the various phases through 

 which the organism passes are described. 



The organism which is considered new, both generically and specific- 

 all}^, is described as follows: 



"Plasmodium parasitic; peridial wall brittle, nonpersistent, shining, breaking in 

 straight lines into small irregular pieces; capillitium fragmentary, formed of a few 

 irregular, branching tubules attached to the lower portion of the peridial wall. 

 11989— No. 5 5 



