SOCIAL LIFE AMONG PLANTS 11 



plants standing widely apart. Thus the competition of plants appears 

 to be effective over a much wider area than has been supposed (Fig. 

 24). 



Competition. — The community life of plants rests upon relations of 

 dependency and commensalism ; its universal and ever present expres- 

 sion is competition. Wherever the struggle for a place in which to 

 germinate and to grow, or to obtain light or food, can be demonstrated, 

 there is competition, there is relationship. 



Competition may be purely mechanical, as in crowding out or grow- 

 ing over or stifling of the weaker by the stronger. It is, in its simplest 

 form, the competition between individuals of one and the same species. 

 But local conditions of climate and soil may be more or less profoundly 

 modified by the vegetation itself, thus affecting the aggressiveness of 

 the combatants. This often happens in the competition between 

 different species or between different plant communities. 



Competition withiyi the Species. — The intensity of the competition 

 between individuals of the same species is greatest in dense stands with 

 high sociability. 



The individuals of a species that are widely apart (soc.^ 1) rarely 

 conflict for space. The first colonizers have the advantage over later 

 arrivals, in having well-rooted individuals established and multiplying 

 by seedlings or by vegetative offspring, before their competitors arrive 

 (Fig. 5). In the competition between individuals, and still more in 

 that between species, the outcome is greatly influenced by the vigor, 

 or rather by the rapidity of the germination of the seeds. The greater 

 the difference in time of sprouting and the denser the seeding the better 

 is the prospect for those first germinating to preempt the space. First 

 comes the conflict for space only, then the struggle for light, and lastly 

 that for nutrients. 



One square meter of the Suaeda martima-Kochia hirsuta association 

 on the shell dunes, along the lagoons of Vic in Southern France, con- 

 tains on the first of May about 2,000 seedlings of the annual Suaeda 1 to 

 3 cm. tall. In late autumn their number is reduced to six or eight 

 fruiting plants. 



The progressive intensification of the ''struggle for existence" is 

 most impressive in many-layered communities. As one of its most 

 striking expressions the natural elimination in a forest may be con- 

 sidered. Morosow (1920) counted on one hectare 1,048,660 ten-year- 

 old beeches. In a fifty-year-old pure stand of the same area there were 

 4,460; in a stand one hundred and twenty years old only 509. The 

 completely closed crowded growth permitted, therefore, only 1 out of 

 ^ Sociability. 



