NATURAL HISTORY OF THE FOREST. 153 



and stands of trees grow, how much useful mate- 

 rial they are capable of producing, and under what 

 conditions the largest amount of the most useful 

 material may be produced most quickly upon a 

 given area, which is the principal aim of the 

 forester. 



As we recognize in the animal or in man cer- 

 tain periods of development which are each char- 

 acterized by progress in certain directions, so we 

 can in the tree individual recognize an infantile 

 stage, the seedling first unfolding the characteris- 

 tics of the plant, and occupied in forming organs 

 of nutrition. This process continues more vigor- 

 ously during the juvenile period or brush-wood 

 stage, when the difference in inherited capacity is 

 most pronounced, some species shooting rapidly 

 upward mostly light-needing species while 

 others first consume considerable time in develop- 

 ing a root system, a basis upon which the future 

 persistent growth can establish itself. During this 

 stage the difference in the rate of height growth 

 of different species is greatest and we can speak 

 of rapid and slow growers. After the juvenile 

 period all species grow more or less alike during 

 the brief adolescent or pole-wood period, the maxi- 

 mum rate of height growth occurring in the tenth 

 to fifteenth year with the light-needing and in the 

 twentieth to fortieth year with the shade-enduring 



cross-section appear as the well-known annual rings, permitting a 

 statement of relation of performance to time. 



