The Ailanto
In many southern parts of the British Isles Ailanthus glandulosa has attained forest stature; but it seems to require more sunshine than it can receive in the average Scottish summer. Loudon, indeed, mentions one at Dunrobin, in Sutherland, which was 43 feet high about eighty years ago; but I have found no trace of that tree in the woods there. There used to be one at Syon 100 feet high, but this has been dead for some years. Elwes and Henry have recorded several in the home counties measuring from 70 to 80 feet in height. Dr. Henry found it wild only in the mountains of Northern China. Elsewhere in China it is cultivated to support a certain species of silk-worm (Attacus cynthia); also a drug is prepared from the root bark; but its timber is regarded as fit only for firing, although in this country it has been found serviceable by wheelwrights. It is said to resemble ash, but is of inferior toughness and elasticity.[16] He, therefore, would be acting very unwisely who, having land suitable for ash, should devote it to growing Ailanthus. Indeed the tree, though handsome and hardy, would hardly deserve attention from British planters, were it not for its admirable fitness for street planting. Except the plane, no forest growth adapts itself so generously to the arid heat, the drought and noxious air of London. For this purpose, it is important that, as the Ailanthus is diœcious, only female trees should be planted; the males exhaling a disagreeable rammish odour. I have never been in Northern China, but I cannot conceive that the splendid pinnate foliage of this tree can be more luxuriant in its native forest than it is in a few of the driest, dustiest London thoroughfares.
The habit of the tree in this country tends to forking, probably because the leader is apt to be nipped by late frost; wherefore, to secure a shapely specimen, timely use of the knife is necessary; which attention, to judge from the trees I have seen, is very seldom paid to it.
The Pines
Except the birch, the Scots pine (Pinus sylvestris) is more widely distributed over northern Europe than any other species of tree, and it shows more indifference than any other to variations of climate. While in Eastern Siberia it sustains without flinching a temperature of 40° below zero (Fahr.), it thrives in Southern Spain under a summer heat of 95°. It seems as much at home in the sun-baked region of Southern France as it is in the perennially humid atmosphere and cool soil of Western Scotland and Ireland.
Yet there are limits to its cosmopolitan endurance. Not long ago I spent a profitable day in the Arnold Arboretum at Boston, Massachusetts, under the guidance of its presiding genius, Professor C. S. Sargent. After wandering for hours amid the luxuriant vegetation of that magnificent park, we stopped beside a mangy, stunted conifer, and he asked me whether I recognised it. I did not; but guessed at hazard that it was the Japanese Pinus parviflora. I was surprised to be told that this was the best that could be done in that country with our own Scots pine. From causes difficult to define, probably similar to those which prohibit the growth of our common ivy in the Eastern United States, this tree resists all attempts to make it at home in that atmosphere.
