16 BULLETIN 475^ U. S. DEPARTMENT OF AGEICULTUKE. 
inch. (See diagram of cross section, fig. 2.) The churn turns at the 
rate of 52 and the cylinder 168 revolutions per minute. One side of 
the chum is fitted with a hinged door to permit the reception of un- 
winged seed and their removal after churning. Three bushels of seed 
can be put through at a time, and about 80 bushels in a day. Each 
bushel will yield 10 or 11 pounds of clean seed, so that the daidy 
capacity of the churn is from 800 to 900 pounds. This device has 
been found unsatisfactory in only one respect. Refuse mixed with 
the seed occasionally breaks out one of the teeth and thisi in turn 
is quite likely to break out several others. It is thought that this 
defect can be remedied by the use of teeth of spring steel. 
Screening and I'anning. 
The final cleaning of seed is done by screening and fanning. Where 
no fanning mill is available, fairly clean seed may be obtained in the 
following manner: First, pass the seed through a wire screen to 
remove the coarser particles, such as pieces of cone scales, twigs, and 
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Fig. 2. — Cross section of wing-remo-ving churn. 
needles, and then through a screen of smaller mesh to remove the 
finer chaff and pieces of broken wings; second, winnow the remaining 
seed in the wind or by bellows or other mechanical devices. 
Seed may be fanned in one of the ordinary farm machines for 
cleaning grain (PL V). They remove practically all broken and 
empty seed as well as much of the resin and other impurities, if the 
draft is properly regulated and the screens with the right-sized mesh 
are used. It is essential that the wings be removed from seed before 
fanning, otherwise many good winged seeds will be lost. Not in- 
frequently, particularly with poorly adjusted machines, the seed must 
be fanned more than once before it is thoroughly cleaned. 
By the use of a grain-grading machine, the extracting plant at the 
Trapper Creek Nursery divides the seed into four different classes. 
The grading is accomplished by means of a fan, so that the classifi- 
cation is b}^ weight. Germination tests of western yellow pine car- 
ried on for 45 days gave a germination of 13J per cent for seed of 
class 1, the heaviest seed; 1 per cent for seed of class 2, the next 
