Periodical Literature. 575 



published his Origin of Species. Air. Zon then elaborates briefly 

 the fact that in no other field of nature may the struggle for 

 existence and of natural selection be studied to such advantage 

 as in the forest, and that, indeed, the art of the forester in its 

 silvicultural operations consists in utilizing and controlling and 

 regulating this struggle and selection. We quote: 



"The regular decrease in the number of trees on a given area 

 with increase in age forms one of the earliest observations of 

 the foresters, who, at a time antedating Darwin, properly gave 

 this process the name of the struggle for existence, the struggle 

 for the necessary growing space. The foresters have discovered 

 the laws governing this process, a process in which almost 95 

 per cent, of all trees that start life in the stand perish, and in 

 the form of yield tables have expressed it quantitatively, have 

 measured and weighed it. The have shown how this struggle 

 for existence varies with the species, climate, drainage and soil 

 conditions, and age of the stand ; that it is more intense, and 

 consequently the differentiation into dominant and suppressed 

 classes occurs earlier with light-needing species than with shade- 

 enduring ones. In a climate most suitable to the species and on 

 favorable situations this struggle again results in more rapid 

 differentiation into dominant and suppressed trees than when 

 the species grow outside of their optimum range and on poor 

 soils. These are elementary and fundamental facts known to 

 foresters for many years. 



"The foresters have not only observed these facts, but they 

 have also furnished an explanation for them. The most favor- 

 able the conditions of growth, the greater is the development of 

 the individual trees ; the earlier, therefore, begins the struggle 

 for space and the differentiation into dominant and suppressed, 

 with the subsequent dying out of the latter. They have followed 

 this process throughout the entire life of the stand, have estab- 

 lished its various degrees of severity, and have discovered its 

 culmination during the period of the most rapid growth in height. 

 This struggle for space and light is the basis of the forester's 

 operations, as only by utilizing and controlling it is he capable 

 of producing wood of high technical qualities, tall cylindrical 

 boles, free of branches, and wood with uniform annual rings 

 possessing great elasticity. 



"The forest is a natural breeding place in which constantly 



