DISEASES OF PLANTS. 365 



the weather conditions are not the primary cause of the destruction of plants, but 

 that it is due to a weakened condition of the vines brought about by attacks of i:)ara- 

 sitic fungi. Tying up the vines too early in the season is not advisable, and the 

 middle of April is believed to be a better time than the middle of March. If delayed 

 until this time there is not the liability to the destructive action of the high, dry 

 winds of the early spring. 



The sun scald of the Japanese plum has been called to the author's attention for a 

 number of seasons, and the disease seems to lie of considerable importance. The 

 trouble begins in longitudinal cracks in the south side of the body of the tree, and 

 continues until the trunk is more or less decayed. The cause of the cracking of the 

 bark is the successive freezing and thawing, which is most marked on the side 

 exposed to the sun's rays. Jt may be prevented by protecting the south side of the 

 tree, by heading the trees low so tliat the tops will shade the body, l)y giving the 

 trees a slight inclination to the south, thus keeping off the full force of the sun, or 

 by sheltering by mechanical means. 



The control of fire blight of pears is said to he one of great practical importance to 

 the fruit growers of Delaware, and the value of pruning is shown. Two spring j)run- 

 ings are recommendeil, the first l)efor(i the l)lossoms open and the second about a 

 month after blossoming, to be followed by a tliird inspection in the fall before the 

 leaves drop, cutting out at tliis time all evidence of blight which may have escaped 

 the previous operation. 



A new bacterial disease of the potato, (i. Delacroix {Bid. Miu. Agr. [Francel, 

 20 {1901), Xo. 5, pi>. lOl.S-lo.lo). — This disease, which has been noted j)reviously 

 (E. S. R., lo, p. 864; 14, \^. 263), is reported upon at some length, the author giving 

 the results of his investigations made at the request of the Minister of Agriculture. 

 An historical statement is given relative to the appearanc^e and distriljution of the 

 disease, which it is believed has long been present in Ireland as well as in Germany. 

 The characters of the disease, which is due to Bacillus solanincola, are described. In 

 addition to attacking the potato, the tomato is said to be subject to the disease, exhib- 

 iting the same symptoms, although being more resistant than the potato. The organ- 

 ism causing the disease is described at length, and it is said that there is frequently 

 associated with it the mycelium of a number of fungi. Among those noted are a 

 species of Fusarium whicli is quite similar to FusarJum lycopersici, the sclerotia and 

 mycelia of a species of Vermicularia and of Torula convoluta, and a sterile form 

 which seems to be identical with Rluzoctonia mhmi. Of these the Rhizoctonia is 

 thought to be the only parasitic form, the others being present as saprophytes. Infec- 

 tion experiments were conducted with the bacteria as well as the fungi, and the 

 disease was produced in stems artificially inoculated with the bacteria, but the 

 experiments with the other organisms gave negative results. The conditions for 

 infection seem to require a humid spring which is late and cold, followed suddenly 

 by very hot, dry weather. Marked differences are noted as to the susceptibility of 

 different varieties of potatoes to the disease, the early ones being particularly subject 

 to injury. Contrasting characters are presented by which this disease may be dif- 

 ferentiated from other fungus and bacterial diseases of the potato. When first dis- 

 covered, the author considered the organism identical with that described by E. F. 

 Smith as causing a bacterial disease of tomato, eggplant, and Irish potato (E. S. R., 

 8, p. 895), but subsequent investigations show that the organism described by Smith 

 develops rapidly and produces a great number of bacteria in the vessels of the plant, 

 but does not produce thyles nor gum, while the organism of the new disease liquefies 

 gelatin in cultures. A series of experiments was imdertaken for the control of the 

 disease, and the author recommends the selection of sound tubers for planting or of 

 tubers from noninfested regions, a 4-year rotation of crops, and the jilantingof entire 

 tubers, whicii should be treated l)efore planting by immersion for an liour and a lialf 

 in a 1 :120 solution of formalin. The plantings should be made as late as i)ossil)le to 

 insure the ripening of the crop. 



