PROCESSING SEED OF GRASSES AND OTHER PLANTS lis 
The speed of the hammer-mill cylinder required to obtain the 
optimum condition of seed can be determined for each kind and lot 
of seed within 50 r. p. m. The seed used in these studies required 
speeds between 600 and nearly 1,200 r. p.m. Cylinder speeds greater 
than the determined optima increase the percentage of injured seed 
and decrease the effectiveness of deawning. 
A hammer-mill screen of correct size is one in which the diameter of 
the perforations is slightly greater than the length of the seed or 
kernel. 
Seed must be fed into the hammer mill at about the full capacity of 
the machine at the determined speed. Feeding at approximately half 
capacity increases the percentage of injured seed and decreases the 
percentage of deawned seed. 
The percentage of seed injured by milling can be held very low by 
attention to speed, screen size, and feeding. ‘The structure of the seed 
of a few species, however, is such that any mechanical treatment will 
cause damage. Among these are bulbous barley and squirreltail, 
in which the proportion of injured seed was approximately 15 and 20 
percent, respectively. 
Processing seed by the method described reduced the weight, the 
percentage of loss in weight depending on the species and the purity 
of the sample before treatment. Loss in weight in all seeds is largely 
compensated by increases in the percentage of live pure seed or the 
number of seeds per pound, or both. 
Processing seed greatly reduces its bulk, the volume of treated grass 
seed being between approximately one-half and one-eighth that of the 
untreated sample, as measured by changes in test weight per bushel. 
This reduction in bulk facilitates both handling and storage. 
The two types of hammer mill compared in these studies proved 
equally effective at the optimum speed for each machine. The data 
indicate that, for medium-sized mills, the periphery speed of the 
cylinder determines the correct operation and show that for machines 
having cylinders of different diameters the speed of the cylinder 
varies inversely about 40 r. p.m. for each inch of increase in diameter. 
The direct cost of processing is low, ranging between 67 cents and 
$1.50 per hundred pounds of original seed. Both milling and cleaning 
were included in the cost of processing because milling facilitates the 
cleaning operation and hence cannot be considered separately. 
