16 THE WORLD OF LIFE 



hedge and ditch banks on roadsides as far as the Sandy Glacial 

 Gravel extends in any direction. It is found in bushy ground, 

 in old quarries and gravel pits, and on the decaying mud-capping 

 of limestone walls. It is exterminated by stock in pasture, unless 

 it is protected by the stinging-nettle or by the fouling of the 

 ground by rabbits. It is apparently never found in meadows. It 

 is even sometimes eaten by cows, when the much-loved Lamium 

 album (the white dead-nettle) is left untouched; but it would 

 seeem to be taken as a corrective or relish rather than as food. 

 It is found so rarely in the open that it would almost appear 

 to be a shade species of bushy ground. 



*' To sum up, Ballota nigra can only survive (in Lincolnshire) 

 when unconsciously protected by man; for its natural require- 

 ments, a bushy, open, limy, lightly stocked soil is practically not 

 to be found.^' 



This careful study of a single species of plant gives us an 

 excellent picture of the struggle for existence on the outer 

 limit of the range of a species, where it first becomes rare, 

 and, when the conditions become a little less favourable, ceases 

 to exist. How this struggle affects the flora of limited areas 

 under slightly different conditions is shown by the same 

 writer's comparison of meadow and pasture. 



Tw^o fields of each were chosen in the same parish and with 

 the same subsoil (Sandy Glacial Gravel) so as to afford fair 

 examples of each. With the one exception of the mode of 

 cultivation they were as alike as possible. Both had at some 

 remote period been ploughed, as shown by faint ridges, but 

 no one living or their immediate predecessors could remember 

 them in any different condition from the present one. The 

 four fields (29 acres together) contained in all 78 species of 

 plants ; but only 46 of these were found in both pasture and 

 meadow. The number of species in each was nearly the same 

 — 60 in the meadows, 64 in the pastures ; 14 species being 

 found only in the meadows and 18 in the pastures. Broadly 

 speaking, therefore, one-fifth of all the species growing on these 

 29 acres became restricted to well-defined portions of them 



