30 Studies in Forestry [CHAP. n. 



generally deeper and more productive, and the climate was less 

 rigorous. 



During the Roman occupation of Britain (A. D. 44-410) 

 many species of trees were introduced from the continent of 

 Europe, including Sweet Chestnut, English Elm, Poplar, and 

 Lime, together with a good many other ornamental and 

 fruiting trees which failed more or less to establish themselves, 

 and never actually attained anything like true forest growth. 

 Even these four species named have only naturalized them- 

 selves to a certain degree ; for they cannot in our climate, and 

 more particularly in that of the northern portion of the island, 

 with its shorter and considerably cooler summer as compared 

 with the south of England, be relied on to produce seed of 

 normal germinative quality. To compensate for this, however, 

 they are richly endowed with the power of throwing out stoles 

 or suckers from the roots, and these are capable of being 

 transplanted like seedlings. 



Of the various other species that are now entitled to rank 

 among our forest trees, Sycamore or Scots Plane, white and crack 

 Willows, and white and grey Poplars were introduced before 

 the end of the fifteenth century ; Spruce, and Cluster Pine 

 during the sixteenth century; Silver Fir, Maple, Horse Chestnut, 

 and Larch during the seventeenth century (although the Larch 

 was not introduced into Scotland till 1727); Weymouth, Mari- 

 time, Cembran, and Pitch Pines in the eighteenth century ; and 

 Austrian, Yellow, and Jeffrey Pines, Nordmann's and Douglas 

 Firs, Menzies Spruce, &c., during the present century. 



The Forest Trees of any country may be considered, from 

 a sylvicultural point of view, as belonging to one or other of two 

 classes ; for they must be either Principal or Ruling Species, 

 forming, or capable of forming, pure forests without any assis- 

 tance from other kinds, or else Subordinate or Dependent 

 Species, which are practically found thriving best in admixture 

 with one or more of the ruling species. 



The terms principal and subordinate are of course here used 



