100 MAINE AGRICULTURAL EXPERIMENT STATION. 



water with a solid stream between the plants. Not infrequently 

 the heading of the plants seems to be hastened by an occasional 

 application of warm water. The marked success of the 

 method of sub-irrigation already outlined will no doubt com- 

 pletely change existing methods. In any case, the atmosphere 

 should be kept moist by frequent spraying of the walks. The 

 leaf surface of the lettuce plant is enormous, and the rapid 

 transpiration in case the atmosphere is very dry will often seri- 

 ously injure the plants. 



The temperature of the lettuce house may be varied consid- 

 erably, though most growers prefer a night temperature of 

 about forty-five degrees and a range of about twenty degrees 

 during the day. In case it is desired to hold a crop in check 

 for some special purpose, the house may be kept ten degrees 

 lower than here indicated. On the other hand, we often force 

 the crop for a short time by increasing the heat. But, in gen- 

 eral, the conditions of temperature should be as nearly uniform 

 as possible. 



Insect and fungous enemies must be closely watched. It is 

 a good plan to strew tobacco stems or tobacco dust on the bed 

 among the plants; and thorough fumigation once or twice a 

 week is indispensable. Whenever a plant is affected with 

 mildew it should at once be removed and the use of sulphur on 

 the steam or hot water pipes is recommended. If the soil is 

 stirred frequently, however, and if there is reasonable care in 

 watering and in maintaining a uniform temperature, we are 

 seldom troubled with mildew. One of the advantages claimed 

 for the practice of sub-irrigation is that there is less liability of 

 trouble from disease. 



The most profitable varieties to grow will depend entirely on 

 the markets available. In New England there is very little 

 demand for any but the cabbage lettuces, of which there is noth- 

 ing better than White Seeded Tennis Ball, or a selected strain 

 of this, known as Rawson's Hot House. Of the curled-leaf 

 varieties, Grand Rapids is most popular. The cabbage lettuces 

 are more difficult to grow than the others and usually command 

 a correspondingly higher price. 



In marketing, the heads are cut off at the surface of the 

 ground and packed in barrels or crates for shipment. Many 



