Scpi. 8, iSSi] 



NA TURE 



445 



Botanique." Tournefort's idea was, however, an advanced one 

 for the age he lived in, and should not be judged by the light of 

 the knowledge of a succeeding century. He had no experience 

 of other latitudes than the few intervening between Paris and the 

 Levant. Humboldt himself did not suspect the whole bearing of 

 the idea on the principles of geographical distribution, and that 

 the parallelism between the floras of mountains and of latitudes 

 was the result of community of descent of the plants composing 

 the floras, not that it was brought about by physical causes. The 

 idea of the early part of the eighteenth century is, when rightly 

 understood, found to be the forerunner of the matured know- 

 ledge of the middle of the nineteenth. 



The labours of Linnaeus, himself a traveller, and whose nar- 

 ratives give him high rank as such, paved the way to a correct 

 study of botanical geography. Before his time little or no atten- 

 tion was paid to the topography of plants, and he was the first 

 to distinguish, to lay down rules, and to supply models for these 

 two important elements in their life-history — namely, their 

 habitats or topographical localisation, and their stations, or the 

 physical nature of their habitats. In his " Stallones Plantarum," ' 

 Linnfeus defines with precision twenty-four stations characterised 

 by soil, moisture, exposure, climate, &c., which, with compara- 

 tively slight modifications and improvements, have been adopted 

 by all subsequent authorities. Nor, indeed, was any marked 

 advance in this subject made, till geological observation and 

 chemical analysis supplemented its shortcomings. In his essay 

 " De coloniis plantarum," published fourteen years after the 

 " Stationes," 2 he says, " Qui veram cunque et solidam plantarum 

 scientiam aucupatur, patriam ipsarum ac sedem cujusque pro- 

 priam baud sane ignorabit," and he proceeds to give an oulline 

 of the distribution of certain plants on the globe, according to 

 climate, latitude, &.C., and to indicate their means of transport 

 by winds, birds, and other agencies. India (meaning the ti-opics 

 of both worlds) he characterises as the region of palms ; the 

 temperate latitudes, of herbaceous plants ; the northern, of 

 mosses, algse, and coniferas ; and America, of ferns ; — thus 

 preparing the way for the next great generaliser in the field.' 



This was the most accomplished and prolific of modem 

 travellers, Humboldt, who made botany a chief pursuit during all 

 his journeys, and who seems, indeed, to have been devoted to it 

 from a very early age. His first work was a botanical one, the 

 " Flora Friburgensis," and we have it on his own authority that 

 three years before its publication, when he was only just of age 

 (in 1790) he communicated to his friend G. Forster, the com- 

 panion of Cook in his second voyage, a sketch of a geogi'aphy of 

 plants. It was not, however, till his return from America that 

 his first essay on Botanical Geography ■* appeared, which at once 

 gave him a vei-y high position as a philosophical natiu'alist. Up 

 to the period of its appearance there had been nothing of the 

 kind to compare with it for the wealth of facts, botanical, 

 meteorological, and hypsometrical, derived from his own obser- 

 vations, from the works of travellers and naturalists, and from 

 personal communication with his contemporaries, all correlated 

 with consummate skill and discussed with that lucidity of exposi- 

 tion of which he w as a master. The great feature of this essay is 

 the exactness of the methods employed for estimating the condi- 

 tions under w hich species, genera, and families are grouped geo- 

 graphically, and the precision w ith which they are expressed. 



This was succeeded in 181 5, and subsequently, by four other 

 essays on the same subject. Of these the most valuable is the 

 "Prolegomena,"^ in which he dwells at length on the value of 



' Artmniiates Acadentk(^, vol. iv. p. 64, 1754. 



2 Ibid. vol. viii. p. 1, 1768. 



3 Between the dates of the writings of Linnseus and Humboldt, two 

 notable works on geographical distribution appeared. One by Frid. 

 Stromeyer (" Commentatio inauguralis sistens Historise Vegetabilium Geo- 

 graphicEe specimen," Gottingen, 1800), is an excellent syllabus of the points 

 to be attended to in the study of distribution, but without examples ; the 

 other is a too general work by Zimmermann, entitled, "Specimen Zoologias 

 Geographicse, Quadrupedum Domicilia et Migrationes sistens," Lugd. Bat. 

 1777. which he followed by " Geographische Geschichte des Menschen und 

 der allgemein verbreiteten vierfiissigen Thiere, nebst einer hieher gehorigen 

 zoologischen Weltcharte, Leipzig, 177S-1783." 



* " Essai sur la Gi£ographie des Plantes," par A. de Humboldt et Aime 

 Bonpland; re'dige'e par A. de Humboldt, lu a la Classe des So. Phys. et 

 Math, de I'lnstitut Nalionale. 17 Niv8se de I'An 13, 1805. 



5 " De Distributione Geographica plantarum secundum Cccli temperiem et 

 altitudinem Monlium, Prolegomena." This appeared in quarto in the first 

 volume of the " Nova Genera et Species Plantarum" in 1815, and separately 

 in an octavo form in 1817. Humboldt's other works en geographical distri- 

 bution are '"Notationes ad Geographiam Plantarum spectantes," 1815 ; 

 " Ansichten der Natur." 180S, and ed. 1, 1827; " Nouvelles Recherches sur 

 les lois qiie Ton observe dans la Distribution des formes ve'ge'tales" (1816); 

 and an article with a similar title in the " Dictionnaire des Sciences Naturelles," 

 vol. xviii p. 422, 1820. 



numerical data, and explains his " Arithmeticaebotanices," which 

 consists in determining the proportion which the species of 

 certain large families or groups of families bear to the whole 

 number of species composing the floras in advancing from the 

 Equator to the Poles, and in ascending mountains. Some kinds 

 of plants, he says, increase in numbers relatively to others in 

 proceeding froin the Equator to the Poles, as ferns, grasses, 

 amentiferous trees, &c. ; others decrease, as Rubiacea;, Mal- 

 vacese, Compositte, &c. ; whilst others still, as Labiata;, Cruci- 

 ferse, &c., find their maximum in temperate regions, and decrease 

 in both directions. He adds that it is only by accurately mea- 

 siu-ing this decrease or increase that laws can be established, 

 when it is found that these present constant relations to parallels 

 of temperature.- Furthermore, he says that in many cases the 

 w-hole number of plants contained in any given region of the 

 globe may be approximately determined by ascertaining the 

 number of species of such families. 



The importance of this method of analysing the vegetation of 

 a country in researches in geographical botany is obvious, for it 

 affords the most instructive method of setting forth the relations 

 that exist between a flora and its geographical position and 

 climatal conditions. 



Humboldt's labours on the laws of distribution were not 

 limited to floras, they included man and the lower animals, 

 cultivated and domesticated, as well as native ; they may not be 

 works of the greatest originality, but they show remarkable 

 powers of observation and reflection, astonishing industry, con- 

 scientious exactitude in the collection of data, and sagacity in 

 the use of them ; he is indisputably the founder of this depart- 

 ment of geographical science. 



No material advance was made towards improving the laws of 

 geographical distribution" so long as it was believed that the 

 continents and oceans had experienced no great changes of 

 surface or of climate since the introduction of the existing 

 assemblages of animals and plants. This belief in the com- 

 parative stability of the surface was first dispersed by Lyell, 

 who showed that a fauna may be older than the land it inhabits. 

 To this conclusion he was led by the study of the recent and 

 later tertiary molluscs of Sicily, which he found had migrated 

 into that land before its separation from the continent of Italy. 

 Just, he adds, as the plants and animals of the Phlegrffian fields 

 had colonised Monte Nuovo since that mountain was thrown up 

 in the sixteenth century ; whence, he goes on to say, we are 

 brought to admit the ctu-ious result, that the fauna and flora of 

 Val de Noto, and of some other mountain regions of Italy, are 

 of higher antiquity than the country itself, having not only 

 flourished l;efore the lands were raised from the deep, but even 

 before they were deposited beneath the waters.^ The same idea 

 occurred to Darwin, who, alluding to the very few species of 

 living quadrupeds which are altogether terrestrial in habit, that 

 are common to Asia and America, and to these few being 

 confined to the extreme frozen regions of the North, adds, "We 

 may safely look at this quarter (Behring's Straits), as the line of 

 communication (now interrupted by the steady progress of 

 geological change), by which the elephant, the ox, and the 

 horse entered America, and peopled its wide extent." ^ 



The belief in the stability of climatal conditions during the 

 lifetime of the existing assemblages of animals and plants was 

 also dispelled by the discovery, throughout the northern temperate 

 regions of the old and new worlds, of Arctic and boreal plants 

 on all their mountains, and of these fossilised on their lowlands, 

 and which discoveries led to the recognition of the glacial period 

 and glacial ocean. , . , 



The first and boldest attempt to press the results of geological 

 and climatal changes into the service of botanical and zoological 

 geography was that of the late Edward Forbes, a naturalist of 

 genius, who, like Touniefort, chose the Levant as the field for 

 his early labours. In the year 1846, Forbes communicated a 

 paper to the Natural History section of this Association, on the 

 distribution of endemic plants, especially those of the British 



" Humboldt's isothermal lines and laws of geographical distribution are 

 obviously the twin results of the same researches, one physical, the other 



'° °I*^do'not hereby imply that no progress was made in the knowledge of the 

 facts of distribution, for, over and above many treatises on the distribution ot 

 the plants of local flor.is, there appeared, in 1816, Schouw s ' Dissertatio de 

 sedibus plantarum originariis ' ' ; which was followed in 1822 by his "cellent 

 "Grundtrack til el almendelig Plante-Geographie,' of which the German 

 edition is entitled, " Grundzuge einer allgemeinen Pflanzengeographie. 



3 " Principles of Geology," ed. 3, vol. iii. p. 376. 1834- . 



4 Journal 0/ Researches in Geology and Natural History. &"<.., p. 15' 



