LETTUCE 209 
erect, as shown in Fig. 71. When properly grown, they 
are crisp and tender, and possess a peculiar piquancy 
which is agreeable to most people. As people become 
better acquainted with Cos lettuce, the demand increases. 
When the heads are nearly mature, the leaves are tied 
together with raffia, which has the effect of blanching the 
interior leaves and making them more crisp and tender. 
Several varieties of Cos lettuce are used for forcing. 
‘Trianon was found most satisfactory in a test at the New 
Hampshire Station. The heads were larger than those 
of other varieties and they were also excellent in quality. 
Among other varieties which are grown to some extent 
under glass may be mentioned Bath, Express, Golden 
Yellow and Dwarf White Heart. 
Cos lettuce does much better as a forcing crop during 
the fall and spring than at midwinter. 
Seed of-the highest quality is vital to success. Only 
the purest strains should be planted, and they should be 
maintained and improved if possible, by making careful 
selections. Some of the most successful greerihouse 
growers produce their own seed and sometimes a surplus 
to sell. When seed production is to be undertaken the 
plants should be set 12 to 15 inches apart in the row and 
there should be ample space between them—not less than 
2 feet—to permit the use of wheel hoes without injuring 
the plants. The seed stalks should be tied to stakes so 
that they will not be blown over by the wind. As soon 
as the seeds are fully developed, the stalks are cut and 
hung in a building to dry. Threshing is easily accom- 
plished by shaking and pounding the plants, and the seed 
is then cleaned by the use of a small windmill, or by 
throwing it up into the air, over a smooth floor or sheet, 
and allowing thé wind to blow away the chaff. 
Inasmuch as lettuce seed retains its vitality for three 
or four years, it is unnecessary to grow seed every year. 
When purchased, sufficient quantity should be obtained 
to last two years or more, and then preliminary tests may 
