17 



characteristic to one familiar with the disease, but much more so 

 is the peculiar, clean cut rotting away of the blades of the outer 

 leaves, leaving a sound, bare stalk. The cause of this is a fungus 

 whose full development is not well understood. It is a species 

 of Rhizoctonia. We have found that in the lettuce house it lives 

 entirely in the soil, producing no spores, and is entirely similar 

 to the real Drop (Sclerotinia) in regard to its susceptibility to 

 treatment. 



-r* Bacterial Diseases of Lettuce. 



References are not uncommon to diseases of lettuce caused by 

 bacteria, but in this section no clearly defined trouble of this sort is 

 at all prevalent. We have found occasionally on weak, poorly 

 grown plants a dying of the leaves which seemed to be caused by 

 bacteria. In these cases the disease was located on the margins of 

 the inner leaves which died or withered along the edge, the affected 

 portion being full of bacteria. This effect was entirely similar to 

 that produced by the physiological trouble known as " Top Burn," 

 with which it is very likely more or less connected. Still there are 

 cases where the rotting continues down into the head leaving only 

 the stump intact, and no organisms but bacteria can be found, so 

 that the principal destruction is apparently caused by them. In 

 well growm plants we have found no such trouble. This appears to 

 be the same disease as that described by Jones, and also by White. 

 The bacterial stem rot mentioned by Jones and the '' Bacteriosis " 

 w'hich Ilalsted speaks of seem to be quite similar to the Drop in 

 effect. We have never met with such a disease. 



METHODS OF CONTROLLING AND ERADICATING THE DROP. 



In the treatment of a disease the first essential is to understand 

 its cause, and when this is a parasitic organism it is of the greatest 

 importance to gain a knowledge of its life-history and its relation to 

 its environment. We have previously pointed out what is known 

 concerning the life-history of the fungus w'hich is the specific cause 

 of this disease, and our methods of treatment must take into consid- 

 eration this knowledge. Since the Drop fungus does not produce 

 myriads of light spores (conidia) similar to those produced by 

 Mildew, etc., but propagates itself by means of mycelium and scler- 



