DISEASES OF PLANTS. 647 



greater rapidity of growth, simplified brancliiug of tlie mycelium, ready pro- 

 duction of oospores, and failure to infect the pear after inoculation, although 

 small cankers were obtained on the almond. 



Factors involved in the growth, and the pycnidium formation of Plen- 

 odomus fuscomaculans, G. H. Coons (U. S. Dept. Agr., Jour. Agr. Research, 

 5 (1916), No. 16, pp. 713-769). — In a paper contributed from the Michigan Ex-' 

 periment Station, the author gives results of experiments performed with 

 P. fuscomaculans, a fungus pathogenic to apple. The specific investigation 

 undertaken was to determine the efCect of various controlled environmental 

 factors upon the growth and reproduction of the fungus. 



The organism was found to have a wider range of conditions suitable to 

 growth than to reproduction. The base level of conditions necessary for growth 

 was found in conductivity water at low temperatures. Reproduction requires 

 more favorable conditions. As a result of these investigations the author 

 believes a basis for practical recommendations as to culture of other organisms 

 has been found, as well as evidence of the feasibility of developing a standard 

 synthetic solution which would make possible a standardization of environ- 

 ments for diagnostic purposes. The author proposes a theory to explain the 

 mechanism of the opposed action of growth and reproduction, in which it is con- 

 sidered that competition for oxygen is the fundamental reason for absence of 

 fructification under conditions which allow abundant growth. 



Preliminary note on leaf invasions by Bacillus amylovorus, F. D. Heald 

 (^yasJlingto)l Sta. Bui. 125 {1915), pp. 3-7, pis. 2).— The results from prelim- 

 inary studies in the field and laboratory on leaf invasions by B. aniylovonis 

 are given which show that this form of attack is rather common. The leaf 

 invasion was first noticed on Bartlett pears at North Yakima, Wash., but soon 

 after similar attacks were found on Wagener, Jonathan, and Rome Beauty apple 

 trees. Later collections were made from both pear and apple trees throughout 

 Washington. Pure cultures were isolated from leaf lesions and used in inocu- 

 lation experiments, and in about eight days seedling trees exhibited typical 

 forms of fire blight. 



Notes on the fire blight disease, V. B. Stewakt (Phytopathology, 5 (1915), 

 No. 6, pp. 327S34). — Notes are given on the influence of commercial fertilizers 

 in developing fire blight, varieties of the pear resistant to the disease, and fire 

 blight as favored by hail injury. 



In the experiments on the use of fertilizers, nursery ground was prepared and 

 planted in 1911, all seedlings of suitable growth being budded in August to 

 Bartlett pears. In the following year the nursery plats were cultivated four 

 times, and in 1913 and in 1914 fertilizers were again applied and the plats 

 cultivated four times. In July, 1914, five trees in each plat were inoculated 

 with a 2-day-old bouillon culture of Bacillus amylovorus, and many infections 

 were apparent within a period of five days. No differences as to the resistance of 

 the trees could be noticed which could be attributed to the fertilizers used. 

 Nitrogen did not materially affect the fire blight by increasing the growth of 

 the trees, nor did phosphates and potash harden the tissues and make them 

 more resistant. 



In discussing varieties of pear resistant to blight, the author calls attention 

 to the varieties Douglass and Sand Pear, which, he thinks, afford material 

 suitable for developing a pear that might have considerable resistance. He 

 does not consider entire immunity as very probable. 



The unusual prevalence of fire blight in New York in the summer of 1914 is 

 considered as associated with a severe hailstorm, the bacteria being carried to 

 the wounds by insects which visited the trees to feed on exuding sap. 



