TREES FOR WATER CATCHMENT AREAS 121 
accelerated by the discovery, in the early part of the nine- 
teenth century, of the trees of the Pacifie Coast region of 
North America, where, in a climate absolutely similar to 
our own, the highest and most valuable type of coniferous 
forest on the planet has been evolved. The Douglas fir, 
Sitka spruce, Abies nobilis and grandis, Thuya gigantea, 
Pinus insignis, and Cupressus macrocarpa are perhaps the 
most important trees from this region. From Asia we have 
introduced the Japanese larch. 
There are numerous other trees, which are occasionally 
used in our plantations, but scarcely any promise to be of 
real value. In fact, the pursuit of new species is over as 
regards commercial forestry. We have all the wild species 
that we need. It is different with regard to trees of hybrid 
origin. Remarkable fastness of growth, far surpassing that 
of wild species of the same genus, is shown by certain 
hybrids of the first generation, or so-called ‘first crosses.’ 
Amongst these may be mentioned black Italian poplar, 
cricket-bat willow, and London plane, all hybrid trees which 
originated as chance seedlings. Fast-growing hybrids of 
trees like ash, walnut, oak, etc., if they could be produced 
by artificial cross-pollination, would be invaluable; and 
efforts to make such hybrids have been attempted. One of 
the most interesting of these artificially made trees is a new 
hybrid poplar, Populus generosa, produced at Kew in 1912 
(see Gardeners’ Chronicle, lvi. p. 257 (1914)). As to the 
quality of the wood of these hybrid trees, I may quote from 
my article on “The Artificial Production of Vigorous 
Trees,” in Journ. Dept. of Agriculture, Ireland, xv. p. 42 
(1915): 
“Tt is a popular belief that fast-grown timber is neces- 
sarily soft and comparatively worthless. This is a fact in 
most conifers ; but in one class of broad-leaf trees, the wood 
of which is characterised by large pores in the inner part of 
the annual ring, the contrary is true, as the faster the timber 
of these trees is grown the stronger and denser it becomes. 
This class includes oak, ash, chestnut, hickory, and walnut, 
the species, in fact, that par excellence produce the most 
