74 PLANT DISEASES 



efficacious against insects and fungus-spores. It is cheaper 

 and more easily employed than either sulphur or Bordeaux 

 mixture. The proportions to be used are 5 grams of lysol 

 to one litre of water. Three applications are necessary 

 spring, early summer, and late summer. 



Viala, Les Maladies de la Vigne, p. 57, figs. 

 Cooke, Gard. Chron.^ Jan. 2, 1894. 

 Prillieux, Malad. des Plantes Agric., vol. i. p. 97, figs. 

 Massee, Gard. Chron., July 21, 1894. 



LETTUCE MILDEW 



(Bremia lactucae, Regel. 

 = Peronospora gangliformis, De Bary.) 



This fungus often proves very destructive to cultivated 

 lettuce, especially when grown in houses, where the con- 

 stantly humid atmosphere favours its development. The 

 leaves become more or less covered on the under surface 

 with an exceedingly delicate white mould, turn yellow, and 

 die, the whole plant being stunted in growth. Chicory 

 and artichokes are sometimes also severely attacked, as are 

 also cultivated cinerarias. 



The fungus occurs on many wild composite plants. 



PREVENTIVE MEANS. Dilute Bordeaux mixture checks 

 the spread of the disease where it can be applied, which is 

 not the case with lettuce. Houses that become infested 

 should not be again used for the forcing of lettuce for some 

 time, lest resting-spores in the soil inoculate the crop. 



This species is very sensitive to a lowering of temperature, 

 and can be checked if the temperature of a house can be 

 suddenly lowered for a short period. 



