conspectus: what governs infection 13 



The parasites of ripened tissues do not require so much 

 water, are able to convert starch into sugar, or have a special 

 liking for some other element of the plant tissue. 



Externally, a number of factors favor infection. One of 

 these is excessive shade, either of clouds or of foliage, and an- 

 other is high temperature. When these two factors are accom- 

 panied by excessive rainfall, high winds, wet earth, and heavy 

 dews, the conditions are ideal for the rapid dissemination and 

 the destructive prevalence of a variety of bacterial diseases of 

 cultivated plants. The bean blight due to Bacterium phaseoli, 

 the angular leaf spot of cucumber due to Bacterium lachrymans 

 (Figs. 6 to 9), the black spot and canker of the plum due to Bac- 

 terium pruni, and the lark-spur disease due to Bacterium del- 

 phinii, are all favored by heavy dews and by shade. In hot, 

 wet weather in midsummer, pear blight due to Bacillus amy- 

 lovorus often bursts out like a conflagration and sweeps over 

 whole orchards. In warm, moist autumns bacterial diseases 

 of the potato may destroy almost or quite the entire crop over 

 extensive districts. 



Fruit Acids found 



Apple Malic only. 



Banana Probably malic only. 



Cantaloupe Malic none — probably all citric. 



Cherry Malic only. 



Cranberry Citric probably predominates — malic also present. 



Currant Citric probably predominates — malic sometimes pres- 

 ent. 



Gooseberry Malic and citric. 



Peach Probably malic only. 



Pear Malic only in some varieties; citric probably predomi- 

 nates in others with small amounts of mahc. 



Persimmon Probably malic only. 



Plum Malic only. 



Pomegranate Probably all citric — no malic or tartaric. 



Quince Malic only — no citric. 



Raspberry (red) Probably citric only — malic, if present, in traces only. 



Watermelon Malic, no citric. 



Jour. Amer. Med. Assoc, vol. Ixix, No. 17, Oct. 27, 1917, p. 1433. 

 Bigelow, W. D., and Dunbar, P. B.: The acid content of fruits, Jour. Industrial 

 and Engineering Chem., 1917 (9, 762). 



