Traces of the Aspen have been discovered in Calcareous Tufa of Neolithic age in Flints. It is found in the Arctic and N. Temperate Zones in Arctic Europe, N. Africa, and N. Asia. In Great Britain it is not found in S. Hants, E. Kent, Monmouth, Cardigan, Lincs, Mid Lancs, Haddington, Linlithgow, Caithness, but elsewhere as far north as the Orkneys, and is probably indigenous, but often planted. In Yorks it is found at 1600 ft. It is a native of Ireland and the Channel Islands.

One seldom finds any Poplars in a really native state in any situation except in woods, for owing to their quick growth they are much planted in hedgerows and plantations. But the Aspen, which grows in damp, moist woods or by water, may well be native in such stations, and it is seldom found in any other habitat, as are the others which are also found in woods.

The Aspen is an erect, rather distantly branched tree, with a rather short stem and slender branches. The bark is grey. The suckers are downy, as also are the buds, which are not clammy. The leaves are sub-entire, nearly round, broadly toothed, smooth both sides. The leaf-stalks are flattened. Those at the top are on long stalks, and are rounded with wavy margin. The radical shoots have short stalks and nearly triangular leaves.

The blade of the leaf is inserted on the vertically flattened leafstalk, hence their tremulous character. Rain falls and runs down the petioles or stalks, where 2 cups catch and hold it, the cells being thin-walled secrete a resin, swelling when moistened, and the cells absorb the moisture, being protected in dry weather by the resinous deposit.

The catkins are cylindrical, with hairy male catkin scales with narrow lobes. The 2 stigmas are divided into two nearly halfway, seared.

The tree is 40-80 ft. high. It is in flower in March till April. The plant is a deciduous tree, propagated by seeds.

Unlike the Willow, with the floral mechanism of which it agrees in most respects, the Aspen is pollinated by the wind, and has no honey. The stamens are more numerous than in Salix, 4-30, the anther-stalks free, the stigmas are slender and 2-4-fid.

The seeds are clothed in cottony appendages to aid in their dispersal by the wind.

The Aspen is a humus-loving plant, growing in a humus or peaty soil.

Several fungi attack the Aspen, especially Melampsora tremulce, and the petioles are galled by Diplosis tremulce. It is attacked also by Exoascus, Tympanis, Lentinus, Hypholoma, Pholiota, Pleurotus, Collybia, Fomes, Polyporus.

It is galled by Saperda populnea and Eriophyes pustulatum. Numerous other insects attack it, such as Saperda carcharias, Mela-soma populi, Cladius viminalis (Poplar Hawk Moth), Smerinthus populi, Dicranura vinula (Puss Moth), Pemphigus bursarius, P. spirothecce, Ortho-stylus bilineatus, Phytocoris populi, Pediopsis nassatus, Idiocerus tremulce, I. fulgidus, I. populi, etc. ursinum, L.). 7. Blueben (Sciua non- scripia, Homu. and Link.).