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 (Lactucci sativa) 
487. History. — This species, which has never been 
found in the wild state, is thought to be a modification of 
Lactucci 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 the 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 and West have found it a satisfactory vegetable 
to grow on a large scale for northern and eastern mar- 
kets. The areas devoted to lettuce are especially large 
in the Norfolk region, at Sanford, Fla., in California, 
New York, and New Jersey. In recent years lettuce has 
been produced extensively on some of the muck soils of 
the North. As a forcing crop, both in frames and in 
greenhouses, it occupies first place in commercial im- 
portance. Lettuce may be found on our city markets 
throughout the year. 
489. Varieties. — Prof. W. W. Tracy (“American Varie- 
ties of Lettuce”) presents the following classification 
and description of the various types: “The classes to be 
