LETTUCE 171 



begins and soon stops the functions of the 

 leaves, causing them to drop and soon dry 

 up. There is no good remedy for this 

 trouble. The rotation of crops probably is 

 the most feasible. 



Downy mildew is sometimes found on let- 

 tuce, generally causing a slight discoloration 

 of the leaf, but as a general rule being of 

 very little injury, as it affects mostly the 

 outside leaves. Good sanitary conditions 

 with plenty of light will remedy this diffi- 

 culty. Leaf spot is sometimes observed on 

 lettuce, but has never been very troublesome. 

 There is no satisfactory remedy. 



There seems to be one other trouble with 

 lettuce which has not been classified as a 

 disease nor as an insect injury. It probably 

 would come under the head of physiological 

 trouble, mentioned by the growers as being 

 white heart. The lettuce seems to grow all 

 right until a certain stage is reached. The 

 outside leaves then seem to separate from 

 the heart, and the leaves turn a light yellow 

 color without forming any compact heart. 

 The plant is never fit to sell. The author 

 has noticed patches where this trouble was 

 present to the extent of 50 to 60 per cent. It 

 is generally found on portions of ground 



