Retrogression of Plant-formations 7 



superficial difficulties in detemuning the nature and lirmrs 

 of these formations, difficulties mainly dne to ktunan inter- 

 ference with natui-al vegetation. 



In the days before the face of the country was changed 

 by the activity of man woodland prevailed over practically 

 the whole area of the types of soil mentioned, with the 

 exception, probably, of parts of the first and last, i.e. of 

 the chalk and limestone and of the poorer sands. At the 

 present day, cultivated crops, "permanent 



Retrogressive pasture" which has been "laid do^vn" and 



changes m , , 



formations. plantations, occupy, of coui-se, the greater 



portion of the country, but apart altogether 

 fi'om these the natural vegetation of each type of soil 

 is actually varied. Besides woodland each type has a 

 characteristic " scrub " or bushland, and a corresponding 

 grassland or, in the case of many sands, a heathland. 



These difEerent types of plant-community on the same 

 soil have no doubt originated mainly from the clearing 

 of the original woodland and the pasturing of sheep and 

 cattle. This prevents the regeneration of the woodland, and 

 of most of the shrubs also, if the pasturing is sufficiently 

 heavy and continuous, while it encourages the growth 

 of grasses. Thus the plant-formation determined by the 

 particular soil, and once represented by woodland, shows 

 a series of phases of degeneration or retrogression from 

 the original woodland, brought about by the activity of 

 . man. The intimate relationship of the various phases 

 (3 iHs©- clearly seen in the associated plants. The woodland 

 proper has of course a ground vegetation consisting of 

 characteristic shade plants, but the open places, and the 

 " drives ' or "rides" of the wood, are occupied by 

 many of the species found among the scrub and in the 

 grassland, while those true woodland plants which can 

 endure exposure to bright light and the drier air out- 

 side the shelter of the trees often persist among the 

 grasses of the open. In some cases where grassland is 



