262 PASTORAL AND AGRICULTURAL BOTANY 



grade seeds, for with improved methods of farming, improvement in the 

 purity of seeds is very rapid. 



The second point is determined in the same way, only particular at- 

 tention is given to the removal of the weed seeds, which may be mixed 

 in the sample. After all the weed seeds and other impurities are removed, 

 their weight is taken and we can then determine the percentage of weed 

 seeds present in the sample. The seed specialist goes further than this 

 and determines the particular kind of weed seeds which are present. 

 Constant practice and a knowledge of the different kinds of seeds will 

 enable him in many cases to determine what seeds are present, but oc- 

 casionally seeds are found, which he is unable to identify. The botanist 

 then has recourse to illustrations and to the collection of seeds, which all 

 well equipped seed laboratories have amassed for the purposes of such 

 comparison. Unless the seed is of an unusual kind, the identification 

 can be made quickly with such aids at hand. Inert matter in some seed 

 tests are included in the final statement, as to the seed impurities. Inert 

 matter includes dirt, stones, chaff, sticks and the like. One of the best 

 laboratories of its kind in the United States is maintained by the Colo- 

 rado Agricultural Experiment Station at Fort Collins, Colorado. The 

 findings of the seed specialist there, as to the chief weed seeds in Colorado 

 crop seeds, may be taken as a sample of the kind of work done in the test- 

 ing of seeds taken from the Second Annual Report of the Colorado Seed 

 Laboratory for 1918. 



The chief weed seeds in Colorado crop seeds are: Wild oats, black 

 bindweed, rough pigweed, lamb's quarters, sunflower, field sorrel, Rus- 

 sian thistle, and green foxtail. Other common weed seeds are wild 

 mustard, Indian mustard, buckhorn, red-stemmed plantain, cow cockle, 

 slender wheat-frass, prostrate pigweed, common ragweed, sedge, large 

 mouse-eare,d chickweed, fetid marigold, barnyard grass, gumweed, pepper- 

 grass, witch grass, spotted smartweed, five-finger, curled dock, pigeon- 

 grass, and buffalo bur. 



There were 188 different kinds of weed seeds occurring as impurities 

 in crop seeds. 



The analyses show the following most common impurities of the im- 

 portant crop seeds sold in Colorado. 



Alfalfa. Indian mustard, dodders, prostrate pigweed, tall pigweed, 

 lamb's quarters, barnyard-grass, sunflower, gumweed, sweet clover, 

 witch-grass, curled dock, Russian thistle, and green foxtail (Figs. 113 and 

 114). 



