DISEASES OF PLANTS. 853 



the leaders were shortened, the laterals being left untouched, showed no 

 bitter pit of the ordinary type. 



At a temperature of 31 to 32° F. in storage, the development of bitter pit and 

 the ripening process were both arrested. 



Canker of fruit trees (Inst. Phytopath. Wageningen, Vlugschr. 13 (1914), 

 pp. 4)- — Nectria ditissi7na is discussed as a wound parasite of fruit trees (apple 

 and pear), also of several forest trees, into wliich it finds entrance only at 

 points of injury from hail, insects, etc. It is controlled by the employment of 

 tree surgery after the cankers have developed, fungicidal sprays, as Bordeaux 

 mixture, being of use only to prevent development from the spore stage. 



The conditions determining- the outbreak of vine mildew in Hungary, G. 

 voN IsTVANFFi (Intcrnat. Inst. Agr. [Rome], Mo. Bui. Agr. Intel, and riant 

 Diseases, 5 {1914), No. 9, pp. 1242-1245). — A summary is given of studies on 

 downy mildew conducted by F. Savoly under the author's direction, and pub- 

 lished in the fifth volume of the publications of the Royal Hungarian Central 

 Ampelological Institute of Budapest. 



It is believed that adequate study of the climatic conditions favorable to 

 mildew will require investigations covering an extensive and varied territory 

 for several years. Satisfactory results require a study of the weather before 

 the first appearance of the mildew, at least as regards temperature and quan- 

 tity and frequency of rainfall. Curves called isophanes have been mapped 

 connecting points of simultaneous appearance of the disease. The successive 

 isophanic belts between these show an increase in breadth, each being about 

 1.55 times as wide as the preceding one. 



During 1910 to 1912 tlie earliest appearance in Hungary was on May 21, 

 most appearances being between June 5 and 15 during the flowering period of 

 the vines, and the infection occurring especially within the last ten days of 

 May. Comparison of the mildew maps during four years shows that the mil- 

 dew occurs in the same locality each year, and its spread follows usually the 

 same routes, this constancy depending more upon orographic and soil relations 

 than upon weather. The mildew generally proceeded more or less continuously 

 from one locality to another, the speed being unequal in different directions, 

 but the same in given directions every year. 



The mildew starts from a definite area described as of triangular form, and 

 advances for a time in approximately the direction of the angles. Independ- 

 ently of this first area, and one or two isophanes later, secondary centers are 

 observed, one of which becomes the point of departure of an independent in- 

 vasion. 



The temperature of the month of April appears to have an influence on the 

 outbreak of mildew. Regularity of temperature changes (with sufiicient mois- 

 ture in winter and spring) favors its early appearance, but repeated relapses 

 in the normal rise of temperature may bring about a retardation of the appear- 

 ance, both frequency and duration of the temperature relapses being apparently 

 influential in this regard. 



An attempt has been made to obtain and express in an equation a " bios " or 

 biological value of the weather as related to mildew outbreak, and the calcu- 

 lated and actual appearance dates as given herein from 1910 to 1913 show a fair 

 degree of correspondence, especially in case of the inner isophanes. A chief 

 condition of complete success for the method is a network of stations in tele- 

 graphic communication. 



According to these researches the districts in which mildew makes its first 

 appearance in Hungary are determined by orogi-aphic and climatic conditions 

 and especially by the nature of the soil and of the conditions of superficial 

 13522°— No. 9—15 5 



