FOREST TREE SEED AND SEED COLLECTING 107 



separated from all fragments of leaves and cone scales. The seed 

 of Eucalyptus and birch usually contain a high percentage of 

 impurities. 



When the seed has a specific gravity greater than unity the de- 

 gree of purity can be roughly determined by placing it in a vessel 

 of water. The seeds sink while the impurities float on the surface 

 from which they can be removed and the percentage determined 

 after drying. 



15. THE AVERAGE PERCENTAGE OF PURITY IN TREE SEED 



From researches conducted at the Swiss seed control station in 

 Zurich, Flury 1 determined the average percentage of purity of 

 certain species to be as follows: 



Per cent. 

 92 

 89 



87 

 85 

 70 

 28 



The table on page 108 gives the average purity of seed purchased 

 in the open market. It is compiled from the author's researches 

 between 1900 and 1910 and the researches of Rafn between 1887 

 and 1912. 



1 Flury, P.: Untersuchungen iiber die Entwickelung der Pflanzen in der 

 friihesten Jugendperiode. (Mitteilungen d. schweizerischeu Centralanstalt 

 f. d. forstliche Versuchswesen, S. 189-202. 1895.) 



