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CHAPTER III. THE ORIGIN OF SPECIES. 



struggle for 134. On all sides around us, in 



existence, nature, the great battle of life is always going on, or, 

 as it is often termed, the struggle for existence. On all 

 sides we find organisms directly destroying others, carni- 

 vorous animals preying on other animals, some plants, such 

 as fungi, killing and feeding on other plants, while every- 

 where animals are found injuring and destroying plants. 

 Not so obvious, but no less severe, is the competition 

 between similar organisms for the same kind of food. This 

 is usually most severe between organisms which require the 

 same food materials and similar external conditions for 

 their existence. To realise this we have only to watch the 

 development of crowded seedlings in a nursery seed-bed, 

 or in the forest. The roots of all are ramifying in the same 

 layers of soil and are competing with each other for the same 

 moisture and the same solutions of mineral salts the stems 

 of all are competing in their endeavours to expand their green 

 leaves in the same light and air. Some individuals are soon 

 seen to be growing more slowly than their vigorous neigh- 

 bours their leaves turn pale, their steins grow weak and 

 finally they die, while the seedlings around soon cover over 

 the gaps caused by their disappearance, leaving no trace 

 of those which have been starved and killed. The Forester, 

 therefore, in order to secure the best development of the 

 individuals belonging to his valuable species, is obliged to 

 interfere in this struggle between plant and plant and to 

 transplant his seedlings and to clean and thin his young 

 woods. Realising, also, that the competition between plants 

 belonging to different species is often scarcely less severe, he 

 takes measures to prevent undesirable species interfering 

 with the healthy development of his valuable trees, while 

 the agriculturist carries out essentially similar operations 

 in his fields, by eradicating the "weeds" which, year after 

 year, appear, in addition to those plants which alone he wishes 

 to cultivate. In order to maintain itself, also, every organism 

 is obliged not only to fight against other living organisms, 

 but, in addition, to struggle against the unfavourable 

 factors of its non-living environment, e.g. climatic influences, 

 great heat and cold, drought, excessive moisture, and so on. 

 The importance and universality of this natural phenomenon 

 of the struggle for existence is perhaps best realised by a 



