4 THE STRUGGLE FOR EXISTENCE 



intraspecies struggle, between individuals of the same species, which 

 in its turn can be divided into a direct and an indirect one. 



(6) In this book we are interested in the struggle for existence 

 among animals, and it is just in this domain that exact data are 

 almost entirely lacking. In large compilative works one may meet 

 an indication that the struggle for existence "owing to the absence of 

 special investigations has become transformed into a kind of logical 

 postulate," and in separate articles one can read that "our data are in 

 contradiction with the dogma of the struggle for existence." In this 

 respect zoologists are somewhat behind botanists, who have accumu- 

 lated already some rather interesting facts concerning this problem. 



What we know at present is so little that it is useless to examine 

 the questions: what are the features common to the phenomena of 

 competition in general, and what is the essential distinction between 

 the competition of plants and that of animals, in connection with the 

 mobility of the latter and the greater complexity of relations into 

 which they enter? What interests us more immediately is the practi- 

 cal question: what are the methods by means of which botanists 

 study the struggle for existence, and what alterations do these meth- 

 ods require in the domain of zoology? 



First of all botanists have already recognized the necessity of 

 having recourse to experiment in the investigation of competition 

 phenomena, and we can quote the following words of Clements ('24, 

 p. 5) : ' 'The opinions and hypotheses arising from observation are 

 often interesting and suggestive, and may even have permanent 

 value, but ecology can be built upon a lasting foundation solely by 

 means of experiment. ... In fact, the objectivity afforded by compre- 

 hensive and repeated experiment is the paramount reason for its 

 constant and universal use." 



However, the experiments so far made by botanists are devoted to 

 the analysis of plant competition from the viewpoint of ontogenic 

 development. The competition began when the young plantlets 

 came in contact with one another, and all the decisive stages of the 

 competition took place in the course of development of the same 

 plants. 



In such circumstances the question as to the causes of the victory 

 of certain forms over others presents itself in the following aspect: 

 By the aid of what morphological and physiological advantages of 

 the process of individual development does one plant suppress another 



