190().] 



PUBLIC DOCUMENT— No. 33. 



137 



Many investigators ^ have carried this process still farther, 

 and separated their seeds by what is known as the specific 

 gravity method. In this case solutions of salt (sodium 

 chloride), ammonium nitrate, sodium nitrate, potassium 

 nitrate and calcium chloride have been used. For this pur- 

 pose solutions of ditt'erent s})eciHc gravities have been made, 

 in Avhich the seeds were placed, first in that solution Avith the 

 highest specific gravity. The seeds which floated in this 

 solution were skimmed off and i)laced in that of the next 

 highest specific gravity, and so on. It has been found that 

 by this method seeds of the same variety, of a uniform, sound 

 condition, difl*er in specific gravities only within a very 

 narrow range. This, however, does not seem to be a very 

 practical plan, as it involves the making of solutions of 

 tested specific gravity and quite a little mechanical manipu- 

 lation. Another method, known as the specific gravity 

 sampling method, is perhaps of less value, as in this case 

 one lot of seed is compared with others in bulk, without 

 separating the poor and undeveloped seeds. It amounts 

 shnply to the choosing of the best lot from several samples 

 of seeds. 



The separation of seeds by sieves would seem to be the 

 easiest and most practical way, and this method with us has 

 given very good results. We used a series of four sieves, 

 having round perforations of 2 mm., 1.5 mm., 1 mm., and 

 .05 mm. respectively. Ten grams of seed were weighed 

 out and run through this series of sieves, with the following 

 results : — 



Table III. — Showing the Res2ilts of sifting Seeds, in which 10 Grams 



were employed. 



' Among whom may be noted V. A. Clarke, New York (Geneva) Experiment 

 Station, Bulletin No. 25(5. 



