CULTURAL DIRECTIONS 351 



set 4 to 6 inches apart, with not less than 12 inches be- 

 tween rows. As the long, white sheaves are the most 

 tender and salable, it is customary to plant the seedlings 

 4 or 5 inches deep in trenches which are gradually filled 

 as the plants grow, or to set them slightly deeper than 

 they stood in the seed bed and hill as the season ad- 

 vances in order to blanch the sheaves. They are also 

 sold green to some extent. Leeks are readily stored like 

 celery in trenches, cold frames, pits and cool cellars. 



LETTUCE (Lactuca saliva) 



487. History. This species, which has never been 

 found in the wild state, is thought to be a modification of 

 Lactuca scariola, which is indigenous to parts of Europe. 

 Asia and Africa. The Greeks and the Romans used let- 

 tuce as a salad, and it is highly probable that the ancients 

 were familiar with its cultivation. 



488. Importance. Lettuce is by far the most impor- 

 tant salad crop grown in t he United States and Canada. 

 It is a standard vegetable in European countries. Mar- 

 ket gardeners in the United States regard it as one of 

 their most profitable crops, and the truck farmers of the 

 South have found it a satisfactory vegetable to grow on 

 a large scale for northern markets. The areas devoted 

 to lettuce are especially large in the Norfolk region and 

 at Sanford, PMa. In recent years lettuce has been pro- 

 duced extensively as a late summer and fall crop in some 

 of the muck soils of the Nor Hi. As a forcing crop, both 

 in frames and in grv, houses, it occupies first place in 

 commercial importance. Lettuce may be found on our 

 city markets throughout the year. 



489. Varieties. Prof. W. W. Tracy ("American Varie- 

 ties of Lettuce," United States Department of Agricul- 

 ture, Bui. 69, p. 12) presents the following classification 

 and description of the various types : "The classes to be 



