98 GRASSES OF IOWA. 



Natural or accidental impurities. — Under this head must be 

 placed the varying amounts of dirt, sand, stick?, deid seed and 

 chaff resulting from improper cleaning, and also the seeds of 

 weeds and weedy grasses which grow naturally, or through 

 introduction, with tne valuable grasses. Of the first series 

 there will always be a small amount in the best cleaned seed. 

 The amount of weed se ds can, however, be easily reduced to 

 practically nothing by pulling up the weeds before the grass 

 seed is harvested. The desirability of any sample of seed is 

 not always fairly indica ed by the percentage of weed seed it 

 contains, for it is readily seen that a small per cent of a very 

 bad weed would be more dangerous than a much larger per 

 cent of a comparatively harmless weed. 



One of the most common weeds whose seeds are found in 

 grass seed is plantain {Plantago major). The lance-leaved plin- 

 tain or rib grass {P. lanceolata) is being rapidly scattered over 

 this country by means of imported grass seed. Other common 

 weeds are sheep sorrtl [Rumex acetoseUa), dock {Rumex crispus 

 et al), shepherd's purse {Capsella hursa-pastoriH), Mayweed- 

 {Anthemis cotula), pigweed {Amarantus sp.), lamb's quarter 

 {Chenopodium album), mallow {Malva sijlvesfris), buttercup {Ran- 

 unculus sp.), and occasionally Canada thistle {Cnicus arvensis), 

 and ox-eye daisy [Chrysanthemum leucanthemum). 



Among the weedy grasses who-e seeds are troublesome may 

 be mentioned the pigeon grasses or foxtails {Chaetochloa viridis 

 and C. glauca). These are especially common i clover seed, 

 hence are apt to get into grass fie ds. Some European seeds 

 contain the seeds of blue pearl gras- {Molinia caerulea) and dar- 

 Lei [Lolium temulentum), two dangerous grasses. Chess or 

 cheat {Bromus secalinus), wild oats {Avena fatua), and sand bur 

 (Cenchrus tribuloides) are also met with. Seeds of many other 

 less harmful or of valuable species are fou d mixed with what 

 should be pure seed of one species. Gilbert H. Hicks* says: 

 "Very few kinds of grass are raised for seed purp ses alone; 

 hence most grass seed is obtained from meadows or places 

 where different species are found growing together." 



The following tables set forth some comparative facts con- 

 cerning the purity of the seeds of four of our common grasses. 

 The first column shows the number of samples of which tests 

 were made. The last three columns show the minimum, aver- 

 age and maximum percentages of pure sted in each series of 



*Pure seed investigations. Yearb. U. S. Depart. Agrll. 1894: 389-408. 



