166 | FORESTS, WOODS, AND TREES 
planted 15 to 20 feet apart, in single or double lines, 
around small fields. The crop of grass or hay is not per- 
ceptibly diminished; and a large volume of timber of 
considerable size and value results from the growth of the 
trees thus isolated. 
The wood of the black Italian poplar is tough and light, 
resisting wear well. It is in demand for special purposes, 
as for brake and slipper blocks, and for polishing plate-glass 
in the course of its manufacture. It is used for beds of 
waggons and carts and for packing-cases. Being uninflam- 
mable to a considerable degree, it is suitable for flooring in 
factories and other buildings. It is now utilised in the 
making of plywood. When well seasoned it is capable of a 
fine polish, and is useful for making cheap furniture. 
There are several other hybrid poplars which have not 
yet been extensively planted in this country. The best 
of these are: (1) Eucalyptus poplar (Populus regenerata, 
Fig. 52), similar in foliage to the black Italian poplar, but 
bearing female flowers. (2) Populus Hugenei, narrower in 
the crown than black Italian poplar ; it makes rapid growth 
on sandy soil at Kew (Fig. 33). (3) Populus robusta, with 
a very narrow crown, thriving at Glasnevin. This promises 
to resist wind better than the other poplars. The history 
and description of these poplars is fully given by the writer 
in Gardeners Chronicle, lv. pp. 1, 46, 66 (1914), and in 
Trans. Roy. Scot. Arbor. Soc. xxx. pp. 14-27 (1916). 
2. Grey poplar (Populus canescens). This tree is not so 
fast in growth as black Italian poplar; but it produces a 
better quality of timber, light in weight and very strong, 
useful for carriage building. This poplar is very hardy and 
may be planted along water courses and in frosty meadows. 
It is not suitable for plantations, but makes a splendid 
standard in coppice on stiff clay soil. White poplar 
(Populus alba) is more sensitive to wind and frost than grey 
poplar, and does not attain so large a size in England. In 
most situations grey poplar is to be preferred as being the 
more vigorous tree. 
" 
3. Aspen (Populus tremula). The aspen is a native tree 
