Effects of Climate and Soil upon Plants—Die Abhängigkeit der Pflanzengestalt von Klima und Boden

Abstract

THIS pamphlet is of greater importance than would be indicated by its mere size, as a contribution towards an investigation of the causes which lead to the diversities of floras, and hence towards a knowledge of the laws on which depends the great problem of the origin of species. M. Kerner has made a special study of the flora of the Tyrolese Alps, and has even attempted to introduce into a small plot of ground in the mountains surrounding Innsbruck, a number of plants indigenous to the lowlands of the Tyrol. In this enterprise, however, he met with no very encouraging success; “the greater number of the plants which I brought to those heights with inexpressible toil, succumbed to the uncongenial Alpine climate; and in the remaining small portion, I have noticed at present only very unimportant changes.” His conclusion from these experiments is “that changed conditions of life can kill the species, or they can reduce it to a starved existence, but can in no case produce a direct change into a new permanent species adapted to its altered conditions.” Such change can only take place by the slow process of natural selection among slightly varying offspring from the parent species. The writer notices a number of interesting features that characterise the Alpine flora with which he is familiar, as contrasted with those found under other climatal conditions. One of these is the very small number of annual plants, which bear to perennials the proportion of 4 to 96, as contrasted with that of 42 to 58 in the Mediterranean district, and of 56 to 44 in that of south-eastern Europe; a result of the very short period of summer warmth, varying from 11/2 to 31/2 months, which does not allow time for the seeds to ripen. The same cause produces also the appearance in many Alpine species of the flower-buds at the close of the summer, ready to burst into blossom during the first days of returning warmth in the spring. The remarkably large proportion of Alpine plants with evergreen rosettes of fleshy or succulent leaves, Primuulas, Gentianas, Androsaces, Saxifragas, Drabas, &c., he attributes to the advantages of some contrivance for obviating the effects of the intense heat of the sun during the long days in their short summers, and also to the necessity that the plant should possess leaves at the very commencement of the warm season, in order to afford it a store of nourishment, and thus economise the whole of the brief period of vegetation. With this peculiarity he contrasts the poverty of the Alpine flora in plants possessing stores of underground nourishment in the form of bulbs, a class so abundant and prominent in the south of Europe. The necessity for great caution in deriving general conclusions from a small array of facts, is shown by the mention by M. Kerner, among the plants well adapted by their constitution to withstand the great alternations of an Alpine climate, of Dryas octopetala, a species which flourishes equally well in the remarkably uniform climate of the west coasts of Ireland and Scotland. The want of any considerable number of large shrubs and forest trees is obviously due to the rigours of the climate; and the almost entire absence of climbing and creeping plants indicates that protection from the sun is not one of the first conditions of existence, as it is in tropical forests. The large proportion of plants with flowers of intense hues, and the deficiency of spiny and stinging species, are not so easy to account for, though the author attributes the latter to the comparative absence of destructive animals; and the former may possibly have some connection with the advantage derived from the speedy attraction of insects, after the flowers expand, to assist in their fertilisation. We can conceive no greater service to biological science than a series of observations on the floras of limited areas, both with respect to what they possess and to what they are deficient in, carried out with the care of those recorded in the work before us.

Effects of Climate and Soil upon Plants.—Die Abhängigkeit der Pflanzengestalt von Klima und Boden.

Von A. Kerner. Pp. 48. (Innsbruck, 1869. London: Williams and Norgate.)