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THE BOOK OF NATURE STUDY 



(Stellar ia media) grow almost everywhere. Many of those given 

 as belonging to calcareous soils are also found on loams, and vice 

 versa. Of course, in actual practice the result of adding lime and 

 manures to arable soils is to modify the " weed flora " that they 

 bear. 



CLASSIFICATION OF SOME COMMON WEEDS ACCORDING TO SOIL. 



PRACTICAL OBSERVATIONS. Arable land, if left uncultivated, 

 would revert to heath. The first stage would probably be a 

 return to rough grass occurring in patches, together with such 

 plants as Ragwort and Crosswort. The former plant sometimes 

 establishes itself to the exclusion of any other. If the soil is 

 sandy the Grass associations might in time be conquered by 

 Bracken and then by Heather. As was seen in the last chapter, 

 natural pasture may be defined as grassland without heath plants. 

 If uncultivated arable land reverts to grassland it is practically 

 only a step further back to grass heaths, and thence to heather 

 moors, or woodland. Thus the vegetation of a district, if undis- 

 turbed by man and animals, is always changing, one species after 

 another being ousted, until at last the one best adapted to the 

 environment creeps in from elsewhere, establishes itself, and 

 holds its own. It is the purpose of vegetation maps to register 

 some of these changes. 



In making observations on arable land, the extent to which 

 Wheats and Oats are cultivated should be noted. In Scotland, 

 Oats are grown wherever land is cultivated at all. An altitude 



