Tree Growing 81 



and in most cases growing unmixed with other kinds. 

 For a long time this was almost the only tree planted. 

 It lines the streets of every town and is largely used 

 for shelter belts on the farms. The result which always 

 follows the unusual increase of a single species has done so 

 in this case. Its enemy has increased in proportion and 

 has done great harm. Professor Fernow, in pointing out 

 this result of growing a single species, says : " a city of elms, 

 for example, is naturally apt to become a city of elm- 

 beetles, the elm otherwise being no more subject to insect 

 pests than many other species which are supposed to be 

 immune, because the opportunity for extraordinary multi- 

 plication of its enemies has not been given." 



Cleanliness of habit, vitality, light and moisture require- 

 ments, shape of crown, amount of shade or value of the 

 wood for fuel, lumber or other purposes, are all things to 

 be considered, and trees should be chosen according to 

 their value for the purpose for which they are grown. 

 Mention of the particular nature of each species in these 

 and other respects will be made when treating them sep- 

 arately, but it must be considered that all trees of the 

 same species are not exactly alike. Great variation among 

 the individuals will be found. 



The two methods of procuring trees are by transplanting 

 them from where they have been growing, or propagating 

 them from seed or cuttings. If they are to be transplanted, 

 the sources are either the natural growth of the woods or 

 stock from a nursery. In some respects the trees from the 

 woods have the advantage. Their adaptation to climate is 



