WEEDS 



471 



and then transfers itself to any neighboring potato plants 

 that are not protected by applications of Paris green or of 

 other poisons. 



A familiar example of a pasture weed poisonous to the 

 lower animals is the common sheep laurel or lambkill. 1 There 

 are a good many plants, such as some members of the Night- 

 shade family, hemp, and some leguminous species, 2 which may 

 produce symp- 

 toms both of 

 intoxication and 

 of poisoning in 

 horses, sheep, and 

 cattle. 



Of the plants 

 which give a bad 

 taste to milk, 

 field garlic or 

 wild onion 3 is the 

 most important. 

 The bulblets of 

 this weed may 

 also impart an 

 onion flavor to 

 flour made from 

 wheat grown in 



fields infested with it. As an instance of the extent to which 

 weed seeds may contaminate commercial samples of useful 

 seeds, the case of red clover may be cited. Inferior lots of 

 clover seed may contain as much as 67 per cent of impurities, 

 largely other seeds, 4 and the average of 84 samples examined 

 at the Iowa station was 5 per cent, or 3 pounds to the bushel. 

 In the red and mammoth clover seed examined at a single 



1 Kalmia angustifolia. 



2 The so-called "loco weeds," mostly species of Astragalus and Aragallus. 



3 Allium. 



* See Bulletin 21, Iowa Agr. Coll. Exp. Sta. 



FIG. 354. Horse nettle (Solarium carolinense) 



A very troublesome weed of the Nightshade family, 



which has spread extensively from the southeastern 



states. One half natural size 



