10 JOURNAL OF THE KO\AL HORTICULTURAL 80(^1 iVr^'. 



out of stone nnd wi^od. l^riclvs nnd morim", willi roinnrknl^lo (livn-.i^'cnces 

 in the results — orgciuH^s \\liu*h nre ronlly due lo tli(^ (•li;ir;ic((MS of 

 the arcliitects, and not to the materials employed. 



If, ho\A-ever, the chemical composition of the soil has so little effect 

 upon the plant, how comes it that such enormous changes have been 

 effected in the tlora of the grass plots of Eothamsted by chemical differ- 

 ences of manuring ? The explanation is to be found in the fact that on 

 these grass plots a very intense struggle for existence is taking place; 

 every species is trying to enlarge its borders at the expense of its neigh- 

 bours, and if it receives ever so slight an advantage in the competition 

 this advantage accumulates from year to year until tlie species becomes 

 dominant. It is the presence of this factor of competition in the 

 Eothamsted grass plots and in Nature which magnifies a small advan- 

 tage or disadvantage until it may become the determining cause of the 

 dominance or the entire disappearance of a given species on a par- 

 ticular soil. In fact, in many cases competition is the chief factor 

 in Nature, and a plant occupies its particular situation solely because 

 it there can escape from what would otherwise be a strangling com- 

 petition. To take a well-known example, the yellow Horned Poppy 

 {Glaucinm luteum) is one of the most strictly localized plants in the 

 British flora. It occupies the shingle banks of our coasts, and, exposed 

 to violent alternations of temperature, fierce sun and wind, spray and 

 drifting sand, it flourishes exceedingly, and would seem to have found 

 conditions particularly congenial. Yet, if we introduce its seedlings into 

 an ordinary rich garden soil, the Horned Poppy develops to an un- 

 precedented degree, and shows by its vigour how much it can enjoy 

 a fat living in comfortable surroundings. In fact, the Horned Poppy 

 does not occupy the shingle bank because it likes it, but simply because 

 it can exist there, whereas the grass and other plants that can crowd it 

 out of existence on ordinary soils are unable to follow. 



" It does not love the shower nor seek the cold — 

 That neither is its courage nor its choice — • 

 But its necessity in being old." 



We must expect, then, in studying the adaptation of plants to 

 particular soils to find no very apparent factors at work. We shall 

 have to look deeply into the requirements of the plant, and try to pick 

 out the comparatively small causes in the soil which act advantageously 

 or disadvantageously, recognizing how operative these small causes can 

 become under the stress of competition. 



