212 THE BOOK OF NATURE STUDY 



of eighteen inches or so. By examining this with acid or by 

 rubbing it up with water, to see whether it is clayey or sandy, 

 it can generally be allotted to one or other of the formations in 

 question. The acidity or otherwise of the soil to litmus paper 

 should also be tested in the field, and notes should be kept on 

 a point that is not indicated either by the map or the examina- 

 tion of the soils in the laboratory, i.e. the wetness or dryness of 

 the land, and whether the wetness is due to a local spring or to 

 a high level of the ground water. A few preliminary walks will 

 give a general idea of the distribution of the vegetation and will 

 indicate certain species as suitable for detailed study. A small 

 selection should be made from these one for the hedgerows, 

 another for the woods, a characteristic grass and a cornfield 

 weed and future walks should be wholly directed to recording 

 the frequency or absence of these particular species from in- 

 dividual pieces of land. The records should be laid down on a 

 rough tracing from the geological map, which, when the area has 

 been thoroughly traversed, will at once show if any correlation 

 exists between the nature of the soil and the occurrence of the 

 particular species. 



In considering the vegetation of different soils the factors 

 that have chiefly to be taken into account are, on the 

 physical side, the supply of water, and on the chemical, the acidity 

 or alkalinity of the soil. Plants are often described as lime loving 

 or lime hating, and though in some cases the carbonate of lime 

 in the soil may have a direct effect for good or evil upon the plant, 

 the really dominant factor is whether the soil contains enough 

 carbonate of lime to keep it in a neutral or even a positively alkaline 

 condition. As regards water supply, plants which frequent soils 

 habitually short of water have devised various methods for reduc- 

 ing transpiration ; the leaf is often constructed so as to expose a 

 minimum of surface, or is covered with hairs or coated with wax, 

 hence the hoary glaucous appearance the vegetation of a really 

 dry region usually presents. Storage organs like bulbs have been 

 devised to carry other plants through regularly recurring periods 

 of drought. Although these structures, designed to save trans- 

 piration, are commonly found on plants growing in dry areas, 

 they also occur where one would least expect them, on plants. 



