664 DISTRIBUTION AS AFFECTED BY MOISTURE AND HEAT. 



the Indies, in South Australia,'at the Cape of Good Hope, and the 

 dry portions of La Plata, Chili, Peru, and the Andes. Xerophilous 

 plants occur likewise in Brazil, the Mediterranean region, some parts of 

 India, China, etc. At the present day they are more widely distri- 

 buted than the Megatherms. In this group are included many Com- 

 positse, Labiatse, Boraginacese, Liliacese, Palms, Myrtles, Euphor- 

 biacese, etc. The most characteristic orders are — Zygophyllaceas, 

 Cactaceae, Mesembryanthemacese, Cycadaceee, and Proteacese. Suc- 

 culent plants abound — Cacti in America, Euphorbias in Africa, Mes- 

 embryanthemums at the Cape. The history of the fossil plants of 

 these districts is very imperfectly known. 



3. Mesotherms (/U.io'os, middle, and ^%/iij, heat), requiring a mo- 

 derate degree of heat (mean annual temperature 59° to 68° F.) with a 

 moderate degree of moisture. This division includes the majority of 

 Mediterranean plants, plants of Northern India at low elevations, 

 plants of China, Japan, California, the Southern States of America, 

 the Azores, and Madeira (including always the mountain plants of 

 those districts), the plains of Chili, Tasmania, and New Zealand. 

 Mesotherms are also met with on the lower slopes of tropical moun- 

 tains. They include many plants with evergreen foliage, Laurels, 

 Magnolias, Campanulas, Cistuses, many Leguminosse, Compositse, 

 Cupuliferse, Labiatse, and Cruciferse. Analogous forms existed in the 

 early tertiary period in Spitzbergen and North America, while the floras 

 of Japan and of the United States were probably nearly identical. 



4. Microtherms (fiixgog, small, and tfsfiaij, heat), requiring com- 

 paratively little heat (mean annual temperature, 57° to 32° F.) 

 Species of our European plains and of the Alps, those of Asia, between 

 the Caucasus and the Himalayas, those of North America, 38° and 

 40° north, and between 60° and 66° of the Southern Hemisphere, 

 plants of Chili, Cape Horn, Kerguelen Land, and the mountains of 

 New Zealand. Herbaceous perennials abound, deciduous trees and coni- 

 fers. The ground now covered by Microthermal plants was previously 

 occupied by Mesotherms and Megatherms, which were extinguished by 

 the glacial epoch. 



5. Hekistotherms (yimgrog, very , little, d'sgfiri, heat). Plants of 

 arctic and antarctic regions, and upper portions of mountainous or 

 temperate regions. They can bear a continued period of darkness, 

 either from being covered with snow, or from their nearness to the 

 poles, where daylight is absent for many months. Mosses, Lichens, 

 Coniferse, CaryophyUaceae, Eosacese, Saxifragacese, are weU. represented. 



6. Megistotherms (fiiyigro;, greatest, ^%a"I, heat). Plants requiring 

 an extreme degree of heat (more than 86° F. mean annual tempera- 

 ture). This is not geographical. Algse, Ferns, and Lycopods of the 

 coal period may have been their representatives in former ages, as 

 the Algae of hot springs are now-ardays. 



