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Cn. XLII.] EQUILIBEIUM IN THE NUMBEE OF SPECIES. 



435 



/ 



All 



the plants of a given country/ says De CandoUe^ in his 

 usual spirited style^ ' are at war with one another. The first 

 which establish themselves by chance in a particular spot 

 tend^ by the mere occupancy of space, to exclude other 

 species — the greater choke the smaller j the longest livers 

 replace those which last for a shorter period j the more 

 prolific gradually make themselves masters of the ground, 

 which species multiplying more slowly would otherwise fill/ 

 In this continual strife, he observes, it is not always the 

 resources of the plant itself which enable it to maintain or 

 extend its ground. Its success depends, in a great measure, 

 on the number of its foes or allies, among the animals and 

 plants inhabiting the same region. 



Thus, for exam 



some 



spreading boughs and dense foliage flourish in the neigh- 

 bourhood. Another, which, if unassisted, would be over- 

 powered by the rank growth of some hardy competitor, is 

 secure because its leaves are unpalatable to cattle ; which, on 

 the other hand, annually crop down its antagonist, and rarely 

 suffer it to ripen its seed. 



Oftentimes we see some herb which has flowered in the 

 midst of a thorny shrub, when all the other individuals of the 

 same species, in the open fields around, are eaten down, and 

 cannot bring their seed to maturity. In this case, the shrub 

 has lent his armour of spines and prickles to protect the 

 defenceless herb against the mouths of the cattle j and thus 

 a few individuals which occupied, perhaps, the most unfavour- 

 able station in regard to exposure, soil, and other circum- 

 stances, may, nevertheless, by the aid of an ally, become the 

 principal source whereby the winds are supplied with seeds 

 which perpetuate the species throughout the surrounding 



Thus, in the New Forest in Hampshire, the young 

 oaks which are not consumed by the deer, or uprooted by 

 the swine, are often indebted to the holly for their escape. 



In the above examples we see one plant shielding another 

 from the attacks of animals : but instances arp. nprhans. Rtill 



tract."^ 



^ Amcen, Acad. vol. vi. p. 17, § 12. 



F F 2 



