12 



pletely dead, thus giving a very characteristic appearance. (See fig. 

 2.) Meantime the mould spreads all over the plant if it is moist, and 

 the interior tissue is found to be completely riddled with it. This 

 trouble passes in most cases for the Drop, though it is not that dis- 

 ease in its most characteristic and destructive form, but, as regards 

 cause, something quite distinct and of an entirely different nature, 

 though the effect is very similar. It can be distinguished in many 

 cases by the peculiar form of affected plants, and almost always by 

 the gray, dusty gro\Vth of Botrytis which appears on them. It has 

 no relation whatever to the soil and can be handled only by running 

 the house skillfully in respect to temperature, moisture, and ventila- 

 tion. This is probably the disease which is referred to by Jones, 

 Galloway, Bailey, Selby, Kinney, and Garman, though it has doubt- 

 less been confused more or less with the true Drop wliich we shall 

 presently describe. In its true form it does not often trouble exper- 

 ienced growers to any great extent as they keep it down by skillful 

 management; still, taking green-house lettuce everywhere, it is very 

 common, and aft'ords by its occurrence or absence a pretty good 

 indication as to the way the crop is being handled, although this test 

 is not infallible as the disease occasionally gets in, even with the 

 best growers. 



Botrytis on the Leaves of Mature Plants. 



Besides the somewhat characteristic cases which have been 

 described, the Botrytis mould often occurs on lettuce, in the head or 

 in the leaves, more or less spoiling it. (See Fig 3.) This often 

 follows the diseases described, or occurs on poor, weak, or old 

 plants. Sometimes it gets down ' into the head, rotting it out com- 

 pletely. In such cases it is usually called "Mildew." This should 

 not and does not occur in well handled crops, except in connection 

 with other more destructive diseases. It can usually be readily dis- 

 tinguished by the characteristic appearance of the fungus. 



The Drop. 



We are not aware that any rot disease of lettuce has ever been 

 described except that caused by Botrytis and a bacterial disease to 

 which we shall allude further on. As has already been mentioned, it 

 became evident very early in our investigation that Botrytis 'nilgaris 



