164 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



The number of broad-leaf species in the eastern region of 

 North America is very great, and many yield valuable timber ; 

 yet very few are worth introducing into our commercial planta- 

 tions. In certain circumstances, Ji/glatis jiigra (black walnut) 

 and Robinia Pseudacacia may be planted with advantage. In 

 some species the timber produced is inferior in quality and 

 quantity to the allied native species. It is thus of no use 

 attempting the cultivation of Quercus rubra and Q. palustris, 

 which could not equal in any way the product of the English 

 oak. Other species are economically useless on account of their 

 slow growth and their rare production of seed, and this depends 

 on the lack of sufficient summer and autumn heat even in the 

 extreme south of England. For this reason all the hickories, the 

 tulip tree, the two species of Catalpa and Prunus serotitia are of 

 no forestry importance in any part of the British Isles. 



In one respect, however, the North American broad-leaf trees 

 are of great interest to us. After their introduction into Europe, 

 several species accidentally gave rise to hybrids that, are now 

 much valued by foresters and arboriculturists. The poplars that 

 are invariably cultivated for commercial timber in France, 

 Belgium and England are of hybrid origin, being crosses 

 between the American Popuhis deltoides and the European 

 Populus nigra. These remarkable trees, which display astonish- 

 ing rapidity of growth, the black Italian poplar {Populus 

 seroti?ia), which originated about 1740, Populus regenerata (1814), 

 Populus Eugenei (1832), and Popuhis robusta (1895), yield 

 enormous quantities of cheap timber, being profitably grown 

 around small fields devoted to hay and pasture. 



The tree most commonly seen in London, Platatius acerifolia, 

 is in all probability a cross between the American and Oriental 

 species of plane, which originated some time before 1703, when 

 it was first described by Tournefort. Remarkable hybrid 

 walnuts have similarly originated in California during the last 

 forty years owing to the growing together in orchards of three 

 species, Juglans nigra, J. regia, and J, californica. One of these, 

 of which I have received a photograph and measurements from 

 the U.S. Forestry Bureau, Washington, has attained at 40 

 years old 100 feet in height and 15 feet in girth. Fast-growing 

 trees like these hybrids, which produce in a short period a large 

 volume of fine timber, are evidently destined to be of great 

 importance in the timber production of the future. 



