LETTUCE 207 
preference. Narrow cement walks between the beds, 
for the convenience of the workmen, are of greater im- 
portance than walls. 
Varieties—Three general classes of lettuce are used 
for forcing purposes, namely, cabbage or compact-head- 
ing varieties, loose-heading varieties and Cos or Romaine. 
Fig. 70.—Grand Rapids lettuce in a large Middle West range. 
Of the solid-heading varieties, White-Seeded Tennis 
Ball or Boston Market (and its various selections) is the 
best known and most largely cultivated in greenhouses. 
It is grown almost exclusively in the large ranges of the 
Boston district. Its chief points of merit are early ma- 
turity, hardiness, fine quality and compact heads with a 
small proportion of outside leaves, thus making it pos- 
sible to set the plants closer together than other larger 
varieties can be planted. 
Improved Keene, also known as May King, is the lead- 
ing variety in the Irondequoit district of New York. It 
is even smaller than Tennis Ball, but does not form such 
a compact head. It may be planted very closely together 
and still make heads large enough to sell by the dozen in 
the Rochester and Buffalo markets. Salamander or 
Black-Seeded Tennis Ball is grown to some extent in the 
greenhouses near Rochester. 
