528 FIELD CROPS 



695. Weeds May Be Injurious to Man. Some weeds 

 are actually injurious to man. They may cause poisoning 

 from contact with them, as poison ivy, or from eating them 

 or their seeds. Wild parsnips are sometimes eaten for the 

 cultivated kind, with disastrous results. The seeds of corn 

 cockle when ground with wheat into flour are poisonous, 

 as are the seeds of some other weeds. 



BENEFITS FROM WEEDS 



696. Uses. While most weeds are injurious, some may 

 be of value under certain conditions. The leaves of dande- 

 lions and the young shoots of the pokeroot are eaten as 

 vegetables. Many weeds furnish pasture of more or less 

 value, though none of our domestic animals except sheep 

 ordinarily eat weeds when the more tender and nutritious 

 pasture plants are available. Sheep eat many kinds of 

 weeds, and are very often useful in keeping down these 

 pests in pastures and along fences. Weeds furnish a cover 

 to land which is not in crop, and may prevent loss of soil 

 fertility by leaching or by erosion. Deep-rooting weeds 

 bring up some plant food from the lower layers of the soil, 

 and leave it on the surface where it is available for crops which 

 follow. They also open passages for the movement of the 

 soil moisture and make it easier for the roots of crops to 

 penetrate the subsoil. Weeds add to the vegetable matter 

 in the soil when they are plowed under and increase the plant 

 food which is available for useful crops which follow. All 

 these purposes are served to better advantage, however, by 

 growing some of our many cultivated plants specially adapted 

 to the particular use. 



697. Weeds Make Cultivation and Rotation Necessary. 

 Weeds are sometimes commended because they make neces- 

 sary the " cultivation of the soil, which might otherwise be 



