344 REpPoRT OF THE HorTICULTURAL DEPARTMENT OF THE 
of the seeds. It also distinguishes between different individuals 
in the same lot. For instance, when a lot of seed is harvested 
some individuals are not quite so ripe as others. These differ- 
ences find expression, to some extent at least, in specific gravity. 
In many cases seeds grown on different soils or in different eli- 
mates are of unequal value for planting. To some extent these 
differences also find expression in specific gravity... The method of 
a series of salt solutions theoretically sorts out from a lot of 
seeds, those best suited for planting, irrespective of the propor- 
tion of them in the lot, whether few or many.. 
It is unnecessary that solutions differ by less than one one- 
hundredth of unity, as is shown by the following facts: (1) 
Except at critical points in the range of specific gravity, there is 
little or no difference in the cultural characters of seeds differing 
by no more than one one-hundredth of unity. (2) Most seeds 
take up water rapidly and in the length of time it takes to make 
a series of experimental separates, some seeds at least will 
change as much as one one-hundredth in specific gravity and 
sometimes more. (3) In skimming the seeds from one solution 
to the next, the solutions are somewhat changed in density and 
are liable to vary as much as one one-hundredth if they are not 
frequently tested. In a few cases, however, the author has used 
solutions differing from each other by only five one-thousandths 
of unity. 
SALTS USED IN MAKING SOLUTIONS. 
There are a number of highly soluble salts that may be used 
in making up these solutions. The present writer has used 
common kitchen salt (sodium chloride), ammonium nitrate, and 
sodium nitrate (Chili saltpeter). Common saltpeter (potassium 
nitrate) and calcium chloride are salts that have been much 
used. One author has used molasses with good results. Sodium 
chloride makes up a solution of a maximum density at room 
temperature in the summer time of 1.20 and will hold up to this 
density unless a very cool day comes. In winter time this solu- 
tion will not hold up above 1.175 to 1.185 according to tempera- 
ture. Hence this solution can only be used for separating seeds 
of less specific gravity than these densities. For denser seeds some 
of the other salts must be used. Ammonium nitrate holds up to 
about 1.31 at room temperature in the summer time and to about 
