16 



BULLETIN" 475, IT. S. DEPARTMENT OF AGRICULTURE. 



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 churn 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 daily 

 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 this! 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 Fanning. 



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 



Fig. 2.- 



ys" 



-Cross section of wing-removing 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 (PI. 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 by weight. Germination tests of western yellow pine car- 

 ried on for 45 days gave a germination of 13^ per cent for seed of 

 class 1, the heaviest seed; 1 per cent for seed of class 2, the next 



