The London planes have been accused of being chief agents in inflicting influenza, bronchitis and catarrh upon the inhabitants of the metropolis. It has been seriously affirmed that when the seed-vessels of the plane break up in dry spring weather, the air is filled with minute spicules which act as an irritant upon human throats and noses. It may be so; but before condemning the trees, without which London would indeed be desolate, it would be well to ascertain first whether the ailments referred to are more prevalent in London during the months when the plane tree is shedding its dry fruit than they are at other times of the year; and second, whether they are more prevalent in London, where there is wealth of planes, than they are in cities where there are no planes, as Edinburgh, Glasgow, Liverpool, Newcastle, etc. Unless this can be shown to be the case, it is difficult to reconcile the fact that London has the lowest death-rate among the cities of the United Kingdom with any mischief arising from the luxuriance of these beautiful trees. [Illustration: HORSE CHESTNUT (_Æsculus hippocastanum_) IN BLOOM] [Illustration: HORSE CHESTNUT FLOWER SPIKE] The Horse Chestnut In one respect the horse chestnut (_Æsculus hippocastanum_) may be reckoned among the most remarkable trees of British woodland, inasmuch as, although it has been found in a wild state only here and there among the mountains of Greece and Albania, where it enjoys a climate widely dissimilar from that of Western Europe, it has a constitution so cosmopolitan as to become thoroughly at home in all parts of our country. It thrives as vigorously on the dry chalk soil of Hertfordshire as on the soaked hillsides of Perthshire, and, given reasonable shelter from violent winds, produces its magnificent foliage and flowers as freely near sea level as it does at Invercauld in Aberdeenshire, where there is, or was not long ago, a fair specimen growing at an elevation of 1,110 feet, not far short of the practical limit of tree growth in Scotland. In 1864 this horse chestnut was 8 feet 7 inches in girth, and was believed to have been planted in the year 1687; therefore, if it still stands, it is now 226 years old. Another sign of the adaptability of the horse chestnut to British environment is the freedom with which it ripens its large fruit and reproduces itself from self-sown seed wherever it gets a chance. The facility with which it does so has caused this tree to be deemed indigenous in many parts of Europe and Asia where it certainly is not a native, but where it has been planted originally on account of its beauty. Further confusion has arisen from the botanists Linnæus and De Candolle having failed to distinguish the Indian horse chestnut (_Æ. indica_) from the Greek species, and having assigned Northern Asia as the native region of the latter.