Postscript xxi 



In concluding our work there are a few points about which I think it advisable 

 to add some explanatory remarks. First, with regard to its scope, it was intended 

 at the outset to include only those trees which attain timber size in the British Isles. 

 It was found, however, impossible in practice to draw a rigid line between the 

 timber trees and the smaller trees, which like shrubs are cultivated for ornament or 

 curiosity. In the case of genera, which comprise both large and small trees as well 

 as shrubs, our treatment has not been logically uniform. All the species of oak in 

 cultivation have been described in detail, because in this genus shrubs are of 

 exceptional occurrence. On the other hand, only the larger maples have been the 

 subject of separate articles, as it was evident that a brief notice would suffice for 

 the shrubby species. In the case of genera of exceptional interest, as Pinus, 

 Juniperus, Cephalotaxus, all the introduced species, even those of small size, have 

 been treated in full. 



The keys for the identification of species are based upon the characters of 

 the twigs, leaves, and buds, and not upon those of the flowers and fruits, as 

 has been usual in botanical works. The latter characters are often not available 

 in the case of trees, the determination of which may be required when they are 

 in the young state, or at some period of the year when flowers and fruit are not 

 present. 



When the preparation of the seventh volume was drawing near a close, we saw 

 that it would be impracticable, without unduly deferring the completion of the 

 work, to include many of the new species that of late years have been introduced 

 from China and Japan. On this account, Eucommia, Tetracentron, Cercidiphyllum, 

 Pistacia, Phellodendron, Idesia, Poliothyrsis, Davidia, etc., have been necessarily 

 omitted. For obvious reasons, I was unable to take up the complete study of such 

 genera as Crataegus, which is almost exclusively composed either of shrubs or small 

 trees that are merely ornamental in character ; and I have limited my account in 

 this case to a full description of the two indigenous species. Generally speaking, the 

 Conifers have been described exhaustively in our book ; but certain rare kinds of 

 which there are only a few specimens of small size in Cornwall and in the mild 

 districts of Ireland, have been left untouched, as Podocarpus, Callitris, Tetraclinis, 

 Widdringtonia, Dacrydium, and Phyllocladus. 



Though, as just explained, all the species of trees in cultivation in England, 

 Scotland, Wales, and Ireland, are not included, yet a vast number have been 

 described, as is evidenced by the Index, which extends over 80 pages. The Index 

 has been compiled with great care, and should prove of service to our readers, as 

 it embraces, in addition to the common names and the usually accepted scientific 

 names, nearly all the appellations which have been applied to the various species 

 and their varieties and sports in countless lists, catalogues, and books. The com- 

 pilation of this synonymy has been a heavy labour and a thankless task. The 

 choice of the correct name of each species has not been always easy. 



As some of the reviews of the published volumes criticise certain names which 

 I have adopted, it will be well for me to explain my views on the vexed question 

 of nomenclature. That in a work of this magnitude, I have refrained from the 



