CHAPTER XIII. 



HISTORY AND BIBLIOGRAPHY. 



Perhaps the best known of the modern German treatises on the 

 subject of weeds is that of Thaer of the University of Giessen on 

 the Agricultural Weeds, in which some 27 species are described 

 with colored figures, methods of extermination being given. Many 

 of the weeds here described, as the sheep sorrel, corn cockle, 

 Canada thistle, quack grass, and horse-tail, are common to North 

 America. This work passed through several editions; the first ap- 

 pearing in 1881 and the last in 1905. 



L. Danger in 1887 published a treatise of 166 pages on the sub- 

 ject of "Weed and Plant Parasites. This work discussed the more 

 important weeds of Germany, frequently giving methods of ex- 

 termination, and numerous notes on the origin of weeds, including 

 also, under the head of Geographical Botany, a list of weeds found 

 in different soils. The following soils are characterized: (1) Gra- 

 velly soils containing 80 per cent of gravel; under this head he 

 names such weeds as the horse weed (Erigeron canadensis) and 

 spurge (Euphorbia peplus). On the whole, however, the list is a 

 short one. (2) Sandy soils, in which there is 80 per cent of sand 

 of smaller diameter than in gravel soils. The weeds found here 

 are awned brome grass (Bromus tectorum), sheep sorrel (Bumex 

 acetosella), common evening primrose ( Oenothera biennis), corn 

 cockle (Agrostemma githago), horse weed (Erigeron canadensis), 

 and spurge (Euphorbia cyparissias) . (3) Loamy soils with some 

 sand, lacking lime. Some of the weeds found here are sow thistle 

 (Sonchus arvensis), Canada thistle (Cirsium arvense), shepherd's 

 purse (Capsella bursa-pastoris) , dandelion, (Taraxacum officinale), 

 wild carrot (Daucus carota) and chess (Bromus secalinus). (4) 

 Clay soils. This class contains only one of our common weeds, 

 namely horse-tail (Equisetum arvense). (5) Marl soils, contain- 

 ing from 5 to 50 per cent of carbonate of lime. The only weed 

 given in this list that we have in Iowa is prickly lettuce (Lactuca 

 scariola). (6) Limy soils, containing more than 50 per cent of 

 calcium carbonate, are represented by some Cruciferae, and 

 Leguminosae. (7) Humus soils, the organic matter consisting of 



