In the author's Alpine Plants of Europe, which dealt chiefly with the plants of the higher Alpine region, it was pointed out that it is impossible to define zones of altitude at all rigidly, even in regard to a small country like Switzerland, and that different authorities had not always adopted the same standards of elevation in speaking of the vegetation of the mountains of Central Europe.

It was stated that it was impossible to give an exact definition of the term ' sub-alpine,' but it could be taken to be the zone from about 3000 feet, where the vine ceases to be cultivated, to about 5000 feet. But it should be clearly understood that any such limitation is purely arbitrary, and that the expressions Alpine and sub-alpine are often used in a very general sense. The vegetation of one valley of say 5000 feet above the sea may be far more Alpine in character than that of another of about the same height in a district not very remote.

Nor is it always possible to do as that great Alpinist and student of the Alpine flora, the late John Ball,1 did. He called the Sub-Alpine Region the Region of Coniferous trees; and the lower Mountain Region the Region of Deciduous trees (whose upper limit often rises to 5000 feet on the southern slopes). But beech forests are also, in certain districts, a great feature of the sub-alpine zone. The very fact that the forest region, and especially the pine forest region, varies so much in different countries of Europe, and also in quite limited districts, prevents such a basis of calculation from being quite satisfactory, though otherwise it has much to commend it.

In Switzerland the Lowland region comprises the plains and the low hills in the north and west. The flora is very similar to that of temperate Northern and Western Europe, including most of France, Germany, Belgium, and the British Isles. But in addition one finds in the Swiss plains and warm valleys a distinct admixture of Southern plants of Mediterranean source. Among them may be mentioned Astragalus Onobrychis, A. monspessulanus, Trigonella monspeliaca, and Centaurea crupina. In the Rhone Valley about Sion, there is a remarkable mixture of Southern plants, such as Buffonia macrosperma, Iris virescens, Tulipa australis, and Ephedra helvetica, which have ascended the great river basin from the Mediterranean, together with sub-alpines which have descended the mountain-sides.

1 "Climate and Vegetation of the Alps," in the General Introduction to the Alpine Guide.

It is remarkable how few species are purely sub-alpine, in that they do not grow in the lowlands or in the Alpine region. The following might perhaps be chosen as typical sub-alpines, characteristic of that actual zone. Actcea spicata, Dentaria digitata, Lunaria rediviva, Cytisus alpinus, Ononis rotundifolia, Saxifraga cuneifolia, Sambucus racemosa, Prenanthes purpurea, Centaurea montana, Veronica urticcefolia, Lister a cor data, Streptopus amplexifolius, and Lilium Martagon.

Among the 850 species described in this volume there are very few, if any, which do not grow in what is commonly understood as the sub-alpine region in Central Europe, if not in Switzerland. But there is so much overlapping that a very large number of these are also found in the Alpine zone, and a considerable number descend to the lowlands. A fair proportion of the Swiss sub-alpines are British plants. If these Alpine and lowland plants were omitted from a book descriptive of what may be called, with approximate accuracy, the more beautiful and interesting flowers of the Swiss woods and meadows, it would be altogether unrepresentative and misleading.

Many Alpine plants have a very great vertical range of altitude; just as others may be confined to quite a narrow zone. Among those species which the writer has noticed growing in the Alps through the greatest vertical range - a range of at least 7000 feet in some cases - are the following: Arabis alpina, Draba aizoides, Cerastium arvense, Lotus corniculatus (up to 9000 feet several times), Dry as octopetala, Potentilla Tormentilla (this ubiquitous plant reaches 8200 feet on the Col du Galibier), Saxifraga stellaris, S. aizo'ides, S. Aizoon, Sempervivum arachnoideum, Antennaria dioica, Leucanthemum vulgare, Campanula pusilla, Primula farinosa, P. viscosa Vill., Gentiana verna, G. ciliata, Calamintha alpina, Linaria alpina, Thymus Serpyllum (up to 9000 feet), Daphne Mezereum, Plantago alpina, Polygonum viviparum, P. aviculare, Euphorbia Cyparissias, Triglochin palustre (found at sea-level in England, in the plains of Switzerland, and up to 8250 feet in Dauphiny), ]uncus bufonius, Scirpus compressus, S. ccespitosus, several species of Carex, such grasses as Poa alpina, P. bulbosa, Agrostis alba, Phleum alpinum, Deschampsia ccespitosa, Festuca ovina and Nardus stricta.

He has also observed the following ferns with a range of from about 5800 to 6800 feet in the Alps, viz.: Cystopteris fragilis (up to 8500 feet), Dryopteris Filix mas, D. spinulosa, Asplenium viride (up to 8800 feet), A. Trichomanes, Polypodium vulgare, and Botrychium Lunaria (up to 8400 feet).

In comparing the flora of Switzerland with that of the British Isles, the most apparent difference is the absence of the maritime element from that of the former country. Even the Sea-thrift (Armeria maritima) which sometimes grows on hill-tops in England, Scotland, and Ireland, is absent from Switzerland, and its place is taken by the larger and more handsome Armeria alpina. But there are one or two maritime plants, such as the Yellow Horned Poppy (Glaucium flavum), which find a suitable home on the sandy shores of the Lake of Neuchatel.

To students of ecology, or plant associations, and to those occupied with the geographical distribution of plants, the absence of certain species from a given area is no less interesting than the presence of others. Let us therefore mention a few types (other than maritime) of plants found in the British Isles which do not occur at all in Switzerland. In the first place we have a few Highland species, such as Saxifraga nivalis and Primula scotica, which do not get so far south as the European Alps. In Ireland there are one or two North American plants, such as Spiranthes Romanzoffiana and Sisyrinchium augustifolium, which occur nowhere else in Europe.