II 



seemed to have the same disease, but with this difference, that the 

 gray mould did not appear upon the surface as before. The affected 

 tissue was full of a fungus, which grew on the surface as a white, 

 cottony growth, with no sign of the gray, dusty appearance of 

 Botrytis. Many more lettuce plants from different places and show- 

 ing a similar disease were then examined and it was found that the 

 same, difference continually appeared. In some the gray Botrytis 

 manifested itself at once, seeming to leave no doubt that it was the 

 cause _of the disease, in others where the trouble appeared to be the 

 same the white mould and no Botrytis appeared. This disease is 

 known by the Boston growers as the " Drop ". It is also called the 

 " Rot " by some. It has been mentioned in several bulletins as 

 caused by Botrytis and all recommendations for its treatment have 

 been based on this idea. Our study of the subject, however, has 

 shown that this is not the case at all in the most destructive form of 

 the disease, but that the terms Drop, Rot, and Botrytis Disease, have 

 in reality included several distinct troubles. These may now be 

 described in detail. 



The Botrytis Rot of Mature Plants. 



The disease described by Humphrey was without doubt a more 

 destructive development of the Black Root, which often occurs. In 

 this case the trouble starts as before with a rotting of the outer 

 leaves at the base by the Botrytis mould, which works down into the 

 stem and causes a black spot at the surface of the ground.* In the 

 regular Black Root it stops here so far as the stem is concerned. 

 But under certain circumstances of management, of which the most 

 active are high temperature with lack of ventilation, high night tem- 

 perature, (which is the worst), and excessive moisture, the fungus 

 does not stop on reaching the stem, but is able to keep on down into 

 it, sending its branches all through it, and producing a general rot- 

 ting and death throughout. When this occurs, the plant, of course, 

 is cut off from the roots and collapses and dies. This does not 

 usually occur with great rapidity, but commonly the outer leaves go 

 tirst, drooping down upon the ground with their bases covered with 

 a gray, dusty growth of Botrytis. In this way all the larger, loose 

 leaves go down flat on the ground while the solid head at the centre 

 remains erect, perhaps for some time, or even after the plant is com- 



