III.] CONFLICT AMONGST BRANCHES. 87 



hood or colony of branches is determined by very much 

 the same conditions which determine variation in inde- 

 pendent plants growing in soil. I believe that the pri- 

 mary and most important determinant of this variation 

 is the variation in food supply, the same which Darwin 

 believed to be the most potent factor in the origination 

 of variations in general. That branch or phyton which 

 receives the most food, because of its position or other 

 incidental circumstance, is the one which grows the 

 largest, has the heaviest and greenest leaves, and, in the 

 end, is the most fruitful. I use the word food to desig- 

 nate not only the supply of nutriment which is derived 

 from the soil, but also that obtained from the air and 

 which is most quickly and thoroughly elaborated in the 

 presence of the brightest sunlight. Thus the uppermost 

 branches of the tree, whilst farthest from the root, are 

 generally the strongest, because they are more freely 

 exposed to light and air and their course is least im- 

 peded. Many branches in the interior of tree -tops are 

 undoubtedly parasites upon the plant colony, taking 

 from it more than they return. 



If the number of the plant -members is determined 

 by circumstances peculiar to that plant, and if there is 

 variation amongst these members in any plant, then it 

 follows that there must be struggle for existence between 

 them. And this struggle differs from the conflict be- 

 tween independent plants in the complex battle for life 

 only in the circumstance that it is more intense or se- 

 vere, from the fact that the combatants are more closely 

 associated. There are weak branches and strong 

 branches, and the survival of the fittest is nature's 

 method of pruning. The strong terminal branch, shoot- 

 ing upwards toward air and sunlight, makes the bole of 



