634 FARM ' SEEDS ' : GENERAL 



fluence on bushel weight. That the composition should largely 

 modify it is obvious if we imagine the seeds when measured to 

 fill up the measure completely without any air-spaces being 

 left between them ; then the weight obtained would be due to 

 differences in the specific gravity of the substances met with 

 in the seeds. If in one, starch preponderated, and in another, 

 fat was the chief constituent, the former would give a heavier 

 bushel-weight under these circumstances than the latter, as the 

 specific gravity of starch is about i'5, while that of fat is only 

 o"9. Flinty grains of the same kind of cereals, have usually a 

 heavier bushel-weight than mealy ones, even when the sizes of 

 the grains are alike. 



The amount of water in the seed alters the weight, the less 

 water the greater it is, so that seeds just harvested are often of 

 less weight per bushel than when they have been kept some time. 

 Unripe samples also are generally lighter than those which are 

 allowed plenty of time to ripen. 



(iii) The bushel-weight is also dependent on the amount of 

 space left unfilled between the seeds or the way in which they 

 are packed in the measure when it is full. 



The chief characters which determine this, are the size, shape 

 and nature of the surface of the seeds. Large seeds of the same 

 shape pack differently from smaller ones. Round seeds, like 

 peas or mustard seeds, lie closer together than long spindle- 

 shaped grains like oats. Moreover, varieties with polished 

 surfaces slide over each other more easily and arrange themselves 

 more closely than those with rough, hairy, or corrugated exteriors. 



The amount of chafif and other impurities and the manner in 

 which the bushel is filled, alters the weight. If the measure is 

 filled by slowly shovelling the seed into it, the weight will often 

 be found very different from that obtained when the seeds are 

 thrown in as rapidly as possible. 



The general opinion that the bushel-weight is always propor- 

 tional to the size of the seed is incorrect. 



