426 SCIENCE PROGRESS 



The great feature of such sands and light loams, from an 

 agricultural point of view, is that they lack lime ; in fact they 

 are frequently so deficient in this substance that they are sour 

 or acid in nature — a state of things that is inimical to growing 

 plants. Such acid soil conditions are reflected in the weed 

 flora by the occurrence of a few very characteristic species 

 which are unfailing indicators of acidity in the soil. The three 

 most prominent of these are the Spurrey {Spergula arvensis), 

 Sheep's Sorrel {Rumex acetoselld) and Corn Marigold (Chrysanthe- 

 mum segetum). Spurrey is perhaps the worst weed that a 

 farmer has to contend with on such a soil. A member of the 

 order Caryophyllaceae, it produces an abundance of seed and 

 spreads very rapidly, forming in many cases a regular under- 

 growth of vegetation. Long J states that if plentiful it may 

 practically suppress spring- and summer-sown crops. Since 

 it cannot grow unless the soil be acid, the most effective way 

 of eradicating this weed is by applying chalk or lime, so reducing 

 the acidity and thus rendering the soil obnoxious to the Spurrey, 

 which dies out under the circumstances. Sheep's Sorrel is more 

 frequently found in pastures than on arable land, though it 

 does occur in the latter to some extent. The Corn Marigold 

 with its bright yellow flowers and rather fleshy leaves is less 

 common ; the tendency among farmers is to associate it with 

 light acid soils of a rather damp character. 



Various other weeds are characteristic of light, sandy loams 

 which are not necessarily acid, the chief of these being various 

 species of Poppy, the Broad-leaved Dock (Rumex obtusifolius), 

 the Red Dead-nettle (Lamium purpureum) and the Wild Chamo- 

 mile (Matricaria Chamomilla). Besides these more characteristic 

 species there are a number of weeds which are chiefly associated 

 with these lighter soils but which also occur with more or less 

 frequency upon other types. 



A special instance of acid soil occurs in an unlikely situation. 

 Away on the top of some of the Wiltshire downs, which are 

 so markedly calcareous, is a thin layer of soil locally known 

 ats " bake," which is very sandy in texture and so totally 

 deficient in lime that it is decidedly acid. This feature of the 

 soil is indicated by the flora, which includes several species 

 characteristic of sour land which are totally absent from the 



1 H. C. Long, " Identification and Eradication of some Common Weeds," 

 Joarn. Bd. Agric. xviii. No. 4, pp. 292-4. 



