28 FARM GRASSES OF THE UNITED STATES 
the most secetitons implement yet invented. Re- 
cleaned blue-grass seed can be sown with this imple- 
ment, but the uncleaned seed should be sown by hand. 
Grass-seeders are frequently attached to grain-drills. 
They answer very well for timothy to be, sown with 
grain, but are-hard to keep in order. There are sev- 
eral cheap grass-seeding machines which scatter the 
seed by mechanical means. They are satisfactory for 
seeds that feed through them readily, but it requires 
some patience to regulate them properly, and the sower 
must walk at a uniform rate or the seed will not be 
scattered evenly. 
Seeds of approximately the same size and weight 
may be mixed before sowing. Very large seeds should 
never be mixed with small ones, or the small seed will 
feed out first. If heavy seeds are mixed with light ones, 
even of the same size, the heavy ones will feed out first 
unless the mixture is kept well stirred. In sowing 
such mixtures it is well to put only a small amount of 
seed in the machine at a time. By this means the 
separation of the heavy and light seeds is largely 
avoided. 
NURSE CROP 
Just why wheat or other grain sown with the 
grasses should be called a nurse crop is not clear. It 
would be more appropriate to call it a robber crop. 
The idea that it protects the grass probably arose from 
the fact that, when the grain is removed in hot, dry 
weather, the grasses are apt todry up. Having been 
shaded and weakened by the grain, they are unable to 
bear the full heat of the sun, particularly when the 
supply of moisture is short and the grain crop has 
