Text-book of structural and physiological botany / by Otto W. Thomé ... and Alfred W. Bennett.

  • Thomé, Otto W. (Otto Wilhelm), 1840-1925.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of structural and physiological botany / by Otto W. Thomé ... and Alfred W. Bennett. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

    456/506 (page 434)
    and the Straits of Magellan, and by the heaths of the Cape of Good Hope and of western Europe. Since one of the main problems of phyto-geography is the inves- tigation of the means by which a plant ensures its existence, a physio- logical system may be contrived, according to the plan prt)posed by Humboldt, m which those organs of a plant which serve for the main- tenance of its life—in other words its habit—are first taken into account; these characters determining to a great extent the natural features of the vegetation. A certain connection can indeed usually be recognised between the external form of the vegetation and the climatal conditions which determine its geographical distribution. On this plan the vege- table kingdom may be divided into the seven following classes :— I. Woody plants ; 2. Succulent plants, such as the cacti ; 3. Climbing plants (lianes) ; 4. Parasites or epiphytes, like the mistletoe ; 5. Her- baceous plants; 6. Grasses ; 7. Cellular plants ; and each of these groups may be divided into a greater or smaller number of sections. In order to obtain an idea of the entire vegetation of the globe, the surface of the earth has been divided by Grisebach into tvventy-foiir natural floras, or regions of vege- tation. Each of these floras is again subdivided into zones, the phyto-geographical character of which is determined by its elevation above the sea-level; a succession of zones being thus obtained, until at length the line of perpetual snow sets a limit to almost all vegetable life. The determining conditions and the actual boundaries of these floras are, however, at present but imperfectly known, [and, indeed, any such division must be considered as very inadequately representing the endless variety and complexity of nature. In all such classifications there is a definiteness and sharpness of outline, which is really an inherent logical defect of all classifications of natural phenomena, rather than a representation of anything that has an exact counterpart in nature]. The districts charac- terised by the occurrence of similar forms and often identical species, occupy as a rule lower zones of elevation with an increase in the latitude [north or south], and advance from elevated regions in lower latitudes to less elevated regions in higher latitudes. Thus a number of species of the Swiss