xxiv The Trees of Great Britain and Ireland 



ground that all species of trees are comparable, in a greater or less degree, as 

 regards their variation, to the remarkable instance of the Douglas Fir, the Rocky- 

 Mountain variety of which differs so much from that growing on the Pacific Coast, 

 while between these two extremes lie a series of intermediate forms. Similar 

 variation is well known in the case of Pinus Laricio, the geographical forms of 

 which behave very differently in cultivation. Such differences probably exist in 

 all species with a wide distribution ; and in the future, care in the selection of seed 

 may be the most important point in sylviculture. 



All the bibliographical references in the work have been checked independently, 

 and no effort has been spared to indicate with accuracy the source of our information, 

 where it is not the result of our own observations. Though in the course of our 

 labours, we have had the benefit of mutual criticism, it should be clearly understood 

 that each of us is only responsible for the parts which are signed by his initials. It 

 would be inaccurate to quote both our names, when only one of us has verified the 

 fact or studied the question at issue. As an example, " Elwes, in Elwes and 

 Henry, Trees of Great Britain, v. 1 1 79," is the correct citation for the account of 

 Cupressus lusitanica in Portugal; whereas, "Henry, in Elwes and Henry, Trees of 

 Great Britain, V. 1183," is responsible for the article on Cupressus arizonica. It 

 will readily be seen, that while the purely botanical part (including the identification 

 of specimens) has been done by me, that the other part, dealing with distribution, 

 history, and cultivation, has been divided in varying proportions between the two 

 authors. (A. H.) 



