laceae in the western hemisphere are limited to the lower Sonoran climatic zone in North America and its corresponding zone in Chili and Argentine. The following is a tabular statement. The semi-tropic xerophilous forms of Gulf distribution occupy the Rio Grande plain in Texas and Mexico below Eagle Pass. Such species also occur in areas of Colombia, Venezuela, Guiana, Brazil, Uruguay, Paraguay and Argentine and in similar areas of the Antilles. Some are undoubtedly sea-coast species. According to BRAY the following plants are illustrations. Sida leprosa. Uruguay, Patagonia, Argentine, Cuba, north to Washington City. Sida hastata A. St. Hil. Argentine, Uruguay, Mexico, Texas, Arizona. Sida anomala A. St. Hil. Mattogrosso, Uruguay, Argentine, Bolivia, Cuba, Florida, Texas, Mexico. Fugosia (Cienfugosia) sulphurea Garcke. Southwest Texas, Mexico, South Brazil, Paraguay. Spergularia platensis Fenzl. Texas to California, South Brazil. Polygala paludosa A. St. Hil. Brazil, Paraguay, Louisiana and Texas. It is appropriate to conclude these comparisons with the floras of extraAmerican regions with an expositions of the extensions southward through the Andes and the antarctic islands to Australia and New Zealand. The examples are not numerous, but they are unmistakable. Mexican Genera and Species of otherwise mainly Andine, Antarctic and Australian Distribution. Genera and Species. Drimys. Colobanthus. Colobanthus quitensis Bartl. Claytonia. Malvastrum spicatum A. Gray. Coriaria thymifolia Humb. & Bonpl. Oenothera. Fuchsia. Oreomyrrhis. andicola Endl. Crantzia. lineata Nutt. Daucus brachiatus Sieber. Nertera depressa Banks & Soland. Flaveria. Microseris. Pernettya. Lucuma. Breweria. Nicotiana. Muchlenbeckia. Mollinedia. Uncinia. Distichlis. Distribution. Andes to Cape Horn, N. Zealand, Paul Islands, Australasia. Andes to Cape Horn, N. Zealand. Southward to Chili and in Australia. Temperate S. America, N. Zealand. Andes, Australia, N. Zealand. « Andes, Tristan da Cunha, Austral- Southward to Chili and in Australia. N. America, Chili, Australia, N. Zea- Chili, Tasmania, N. Zealand. Polynesia. Andes to Patagonia and the Falk lands and in N. Zealand. Andes, Australasia, Polynesia. S. America, N. Caledonia. W. Indies, Andes, Antarctic islands, Andes, Australia. The foregoing list shows that there is a connection between the antarctic and andine floras, a connection that is more evident when the comparison is made to include American plants not extending northward to Mexico. The most pregnant fact, according to HEMSLEY, is that the genera are almost without. exception much more strongly developed in America than they are in Australasia and the antarctic islands. But if we take the vegetation generally of the southern coldest zone and regions, the preponderance of what may be called American types, in contradistinction to those which are more fully represented in the Australian region is not so great. Chapter V. North American Phytogeographic Classifications. Rehearsing the classifications which have been made of the phytogeographic regions of North America, one of the first most consistent attempts is presented in MEYEN'S Grundriss der Pflanzengeographie (1836),') translated by MARGARET JOHNSTON into English and published by the Ray Society in 1846. Meyen divides the horizontal range of vegetation into zones and the phytogeographic regions are consciously included in these world encircling zones, viz., equatorial zone; tropic zone; sub-tropic zone; warmer temperate zone; colder temperate zone; sub-arctic zone; arctic zone, and polar zone. The vegetation of North America is referred in the most general way to these several zones, which are more or less determined by the temperature of the air and not by the physiographic character of the country. His division based on the vertical range of vegetation need hardly be referred to here. Under the notion of separate centers of development, the most important classification of the land areas of the globe into vegetation regions is that of GRISEBACH. By this writer twenty-four regions are recognized, the following only concerning this discussion, viz., I. Arctic Region. XII. Forest Region of the Western Continent. XIII. Prairie Region. XIV. Californian Coast Region. XV. Mexican Region. XVI. West Indian Region. XVII. Cisequatorial South American Region. ENGLER) divides the surface of the globe into four principal realms (Florenreiche), each of these into regions and each region into provinces, according to his theories of general development and migration. The regions of the continent of North America come under two realms. The regions and provinces where published by this well known author in a new form in 1902 (see P. 344). 1) Confer the Bibliography p. 46-51. 2) ENGLER, A.: Versuch einer Entwicklungsgeschichte II: 334-347; also MACMILLAN, C.: The Metaspermae of the Minnesota Valley, 1892, p. 589. DRUDE) gives the following useful summary of the vegetation-regions of North America transcribed in the original German. 1. Gletscherwald- und Strauchregion von Alaska mit arktischer Glacialflora. 2. Die Kanadische Waldregion. 3. Waldregion des nordamerikanischen Seengebietes. 4. Columbische Küstenwaldregion. 5. Die Wald- und Hochgebirgsregion der nördlichen Rocky Mountains. 7. Die Missouri-Prairie region. 8. Steppen- und Salzwüstenregion der Rocky Mountains. 9. Kalifornische Niederungs-Bergwald- und Hochgebirgsregion. 10. Sommergrüne Laubwaldregion des Mississippibeckens. 11. Die immergrüne Vegetationsregion der südatlantischen Staaten. 13. Chaparal-Vegetationsregion von Texas und Nordmexico. 14. Die nordmexicanische Bergwald- und Hochgebirgsregion. 15. Mexicanische Übergangsregion zu Californien und Texas. 16. Mexicanische subtropische Bergwaldregion (Tierra templada). 17. Mexicanische Hochgebirgsregion (Tierra fria). 18. Mexicanische subtropische Steppenregion. 19. Die tropische und subtropische Vegetationsregion von Nicaragua und Costa Rica. a) Die dürre Croton- und Cacteenregion. b) Die antillanische Tropenregion. c) Die antillanische Bergwaldregion. d) Die antillanische Hochgebirgsregion. MERRIAM 1898 states that the northward distribution of terrestrial animals and plants is governed by the sum of the positive temperature for the entire season of growth and reproduction, and that the southward distribution is governed by the mean temperature of a brief period during the hottest part of the year. Applying these principles, Merriam divides North America into three primary transcontinental regions (better to be named «zones), viz., the Boreal, the Austral and the Tropical. The distinctive temperature of the three boreal zones (Arctic, Hudsonian and Canadian) are not positively known, but the southern limit of the boreal, as a whole, is marked by the isotherm of 18° C. (64.4° F.) for the six hottest consecutive weeks of the summer. It seems pro bable that the limiting temperature of the southern boundaries of the Hudsonian and Arctic zones are respectively 14° C. (57.2° F.) and 10° C. (50° F.) for the same period. Transition zone species require a total quantity of heat of at least 5.500° C. (10,000° F.), but cannot endure a summer temperature the mean of which for the six hottest consecutive weeks exceeds 22° C. (71.6° F.). The northern boundary of the transition zone is marked by the isotherm showing a sum of normal positive temperatures of 5.500° C. (10.000° F.), while its southern boundary is coincident with the isotherm of 22° C. (71.6° F.) for the six hottest consecutive weeks. The transition zone comprises according to Merriam three principal subdivisions; an eastern, or Alleghanian humid area; a western arid area, and a Pacific coast humid area. 1) DRUDE, OSCAR: Handbuch der Pflanzengeographie, 1890; cfr. Atlas der Pflanzengeogr., Bibliography, p. 40. The Upper Austral species require a total quantity of heat of at least 6.400° C. (11.500° F.), but apparently cannot endure a summer temperature the mean of which for the six hottest consecutive weeks exceeds 26° C. (78.8° F.). The northern boundary of the Upper Austral zone, therefore, is marked by the isotherm showing a sum of normal positive temperatures of 6.400° C. (11.500° F.), while its southern boundary agrees very closely with the isotherm of 26° C. (78.8° F.) for the six hottest consecutive weeks. MERRIAM1) recognizes two principal subdivisions of this zone, viz., an eastern or Carolinian area and a western or upper Sonoran area. The lower austral species require a total quantity of heat of at least 10.000° C. (18.000° F.). The northern boundary of this zone, therefore, is marked by the isotherm showing a sum of normal positive temperature of 10.000° C. (18.000° F.). This zone comprises an eastern or Austroriparian area and a western or lower Sonoran area. Tropical species require a total quantity of heat of at least 14.400° C. (26.000° F.), and, since the tropic life region is a broad equatorial belt, it is probable that both its northern and southern boundaries are marked by the isotherm showing a sum of normal positive temperatures of 14.400° C. (26.000° F.). CLEMENTS) proposes a classification of the phytogeographic divisions of North America and emphasizes the importance of using the Latin equivalents (f. ex. zona polari-nivalis, provincia alaskana, prov. cordillerana etc.) in order to avoid mistakes and to preserve a uniformity of treatment in phyto-geographic treatises. The following tabulation, omitting the latin names, represents his views on the subject. Polar-nival Zone. Arctic-alpine Zone. Arctic Prov., Alpine Province. Alaska Prov., Mountain Prov., Ontario Province. Atlantic Prov., Appalachian Prov., Nebraskan Province. Utah Province, with Nevada and Mohave Region. Litoral Province, with Columbia and California Region. Subtropical Zone. Florida Prov., Mexico Province. Tropical Zone. Antilles Prov., Andean Province. The most complete and satisfactory classification of the phyto-geographic regions of North America is one published by ENGLER 3) in 1902 in a brochure which while primarily intended as a guide to the American plants in the new royal botanic garden at Dahlem-Steglitz near Berlin, is much more, because it gives an account of the characteristic plants and peculiar vegetation of the regions given below in the classification printed in the original. 1) MERRIAM, C. HART: Laws of temperature Control. Dec. 1894. Also: Life Zones and crop Zones of the United States. 1898. (Bibliography, p. 49.) 2) Clements, Frederic E.: A system of Nomenclature for Phytogeography 1902. (Bibl., p. 46.) 3) See Bibliography, p. 47. |