II 



DISTRIBUTION OF SPECIES 15 



by cows, when the much-loved Lamium album (the white dead- 

 nettle) is left untouched ; but it would seem 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 requirements, 

 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. 



Two 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 according as 

 these portions were grazed by farm stock or regularly 

 mown for hay. 



Again, Mr. Woodruffe-Peacock states, that the assem- 

 blage of plants that form pasture-lands not only varies 

 with every change of soil and climate, but also with any 

 change of the animals that feed upon them ; so that any 

 one experienced and observant can tell, by the presence of 

 certain plants and the absence of others, whether horses, 

 cattle, or sheep have been the exclusive or predominant 

 animals that have grazed upon it. 



