340 HOW CROPS GROW. 



7. The weight of wheat per bushel depends upon 

 many circumstances, and bears no constant relation to 

 the density of the seed. 



The densest grains are not, according to Church, 

 always the largest. The seeds he experimented with 

 ranged from sp. gr. 1.354 to 1.401. 



Marek has shown that specific gravity is no universal 

 test of the quality of seed, for while, in case of wheat, 

 flax, and colza, the large seeds are generally the denser, 

 the reverse is true of horse-beans ( Vicia faha) and peas 

 {Vs. St., XIX, 40). 



The Absolute Weight of Seeds from different 

 varieties of the same species is known to vary greatly, 

 as is well exemplified by comparing the kernels of com- 

 mon field maize with those of "pop corn." Similar dif- 

 ferences are also observable in different single seeds from 

 the same plant, or even from the same pod or ear. Thus, 

 Harz obtained what were, to all appearance, normally 

 developed sieeds that varied in weight as follows ; 



PKOM SINGLE PLANTS. Milligrams. 



Wheat, Trltieum vulgare, from 15 to 3T 



Wheat, Trltieum polonicum, « 21 to 55 



Barley, Hordeum distichon, " 31 to 41 



Oats, Avena sativa, u jg ^o 30 



Maize, Zea Mays cinquantino, " 169 to'201 



Pea, Piswm sativum, •> 143 to 552 



FBOM SINGLE FKUIT (PODS). 



^^^' from 309 to 473 



^^t";^^' " 33 to 66 



^"P™' " 486 to 639 



Differences often no less marked are found among the 

 seeds in any considerable sample, gathered from a large 

 number of plants and representing a crop. Kobbe, with 

 great painstaking, has ascertained the average, maxi- 

 mum and minimum weights, of 180 kinds of seeds, such 

 as are found in commerce or. are used in Agriculture, 

 Horticulture, and Forestry. The following table gives 

 some of his results : 



