266 PASTORAL AND AGRICULTURAL BOTANY 



shape of the vessel. Small sized, or withered seeds give a smaller vol- 

 ume weight than large plump seeds. The number of seeds in any measure 

 increases with the volume weight and the weight of the individual seeds 

 decreases in like ratio. With cereal seeds the absolute weight of the 

 individual seeds invariably increases with the volume weight. Chemical 

 analyses show that the higher the volume-weight ,the better the edible 

 quality of cereal, or starchy seed. Hence it is important to determine the 

 volume weight. 



To estimate the real, or agricultural worth of a seed sample, we must 

 combine the purity and viability percentages, thus: 



Viability X Purity . 



- = Real, or Cultural Worth in terms of per cent. 

 100 



Means of Detecting Source of Seeds. It is important to have a 

 reliable means of detecting the source of supply of seeds. Wittmack was 



FIG. 119. Wild carrot, c, natural size; a, b, front and edge views. (Taken from 

 Seed Testing its Uses and Methods, North Carolina Agricultural Experiment Station Bull. 

 108, 1894.) 



the first scientific man to interest himself in this question, and in 1873, he 

 recognized a red clover as American owing to the presence in it of seeds of 

 Ambrosia. Sometimes the appearance of the seed itself the metallic 

 lustre of its coat- proclaims its origin. Stebler calls those weed seeds 

 which indicate the origin of the seed source indicators. Other seeds not as 

 reliable, but still helpful, he calls companion seeds. Of the weed seeds 

 found in red clover a few such as ragweed, spurge, field dodder, Practed 

 and black-seeded plantains, spiny sida, lady's thumb and vervain indicate 

 the American origin of the seed in other words are source indicators. On 

 the other hand clover dodder (Fig. 120), scentless chamomile, wild mad- 

 der and ox tongue indicate imported seed. Stebler recognizes the follow- 

 ing" seed supplying districts of the world and the source indicators. 



i. South European (South France, Italy, Spain). Coronilla scorpi- 

 oides and Ammi majus. 



