15 



lettuce house. The sclerotia are mostly of very small 

 size and act simply to carry the fungus over from crop 

 to crop and from season to season. When first formed 

 they make no growth, but after a period of rest and 

 dryness they send out the mould-like growth which 

 soon finds and attacks the plants. This destructive 

 organism is not limited to lettuce, as we have seen pig- 

 weed and buckwheat in a lettuce bed killed by it, audit 

 is kncwn to attack many other plants. Among green- 

 house vegetables it causes the Timber Rot of cucum- 

 bers, sometimes attacks tomatoes, (though we have 

 grown tomatoes in an infested lettuce bed without 

 any trouble), and is quite often seen on water cress Ponn'of sciei- 



and parsley as a dense, white mould. otium produc- 



ing spores. 



This disease appears to have been thus far entirely overlooked by 

 all who have studied lettuce troubles, yet there is no doubt that it is 

 causing to-day far more destruction of green-house lettuce. in Massa- 

 chusetts than any other. It is an active, vigorous parasite, attack- 

 ing and always killing every plant with which it comes in contact, 

 destroying strong and weak alike. The ordinary details of green- 

 house management have very little effect upon it and recommenda- 

 tions of this nature have no practical value. It is found in the 

 houses of ihe most skillful lettuce growers unless some special treat- 

 ment has been applied. On the other hand we have proved bevond 

 doubt that in its method of reproduction and spreading, this fungus 

 is strictly limited to growth in the soil, which fact being known, its 

 extermination in the house becomes a simple matter, the compara- 

 tive economy and practicability of methods being the only uncertain 

 question. \Mien once recognized, this disease can almost always be 

 distinguished from the attacks of Botrytis by ordinary observation. 

 By more technical methods the distinction is absolute. The pres- 

 ence of the dusty growth of spores almost always characterizes the 

 Botrytis. In the other case the white mould is seen at the base of 

 the plant, rotting the leaf bases and stem and spreading in a luxuri- 

 ant growth to the soil, which does not occur with Botrytis. Further 

 than this, Botrytis-affected plants usually go down more slowly, the 

 head remaining upright, while in the real Drop the plant collapses 

 completely in a day or two. 



