GEOGRAPHICAL DISTRIBUTION OF PLANTS AND ANIMALS. 53 



grow in it ; and what is good for one is bad for another. Kocks favor 

 certain plants ; and, in some instances, differences in rocks adapt them to 

 different species of Lichens and Mosses. As the composition of the air, 

 earth, or water varies, the inhabitants differ, what is death to one being 

 life to another. 



The general principle that all living species must have food and just the 

 food they need, or die, is one of tlie foundations for the differences in lim- 

 itation under all the causes above mentioned. Geological changes that vary 

 these conditions have therefore been a great means of determining distribu- 

 tion, by varying temperatures, climate, and land level ; by varying soils and 

 converting deserts into dry land, marshes, or seas by joining lands through 

 .change of level, so as to favor or compel migration ; or sinking them, to the 

 extermination of species. In addition, as Darwin has shown, the changes 

 brought about in the associations of species, in these ways and through their 

 mutual dependence as to food and all necessities, have been other ceaseless 

 causes of variation in distribution. Those continental lands that are most 

 isolated, like Australia and South America, have, for the reasons mentioned, 

 and others, the largest number of peculiar species, and hence the most 

 homogeneous population. 



BRIEF EEVIEW OF DISTRIBUTIONAL FACTS OF GEOLOGICAL INTEREST. 



Terrestrial Species, 



1. Plants. 



Plants of the land spread to all heights, even above the snow-limit. Among Cryp- 

 togams, Ferns and Lycopods flourish in all latitudes from the equator to the polar lati- 

 tudes ; but Tree Ferns, not beyond the parallel of 35°. Under the warm moist climates of 

 tropical and warm-temperate latitudes, Ferns and Lycopods grow in greatest numbers and 

 luxuriance. Palms have their limit in South America in latitude 36°, in North America 

 and Australia in 3-5°, and in Asia in 34°; in Europe one species, Chamoerops humilis, 

 extends as far north as latitude 44°. 



The Conifers range through all zones. The Yews, as Salisburia, live in warm-temper- 

 ate latitudes. But the subdivision of Cycads is confined to tropical and warm-temperate 

 latitudes. They occur in southern Asia, Japan, the East Indies, Madagascar, Australia, 

 southern Africa, and tropical America, including Mexico and the West Indies. 



2. Animals. 

 Australian characteristics. — Australia, although near the East India Islands, ife 

 remarkable for the absence of all ordinary or placental Mammals except Bats of the genus 

 Pteropus, Rats, and Mice. Instead, it has a large population of Marsupial Mammals, the 

 diversified types of ordinary Mammals being represented under the Marsupial or pouched 

 structure. Wallace, in allusion to the diversity among them, says (Geogr., i. 391) : 

 "Some are carnivorous, some herbivorous; some arboreal, some terrestrial; there are 

 insect-eaters, root-gnawers, fruit-eaters, honey-eaters, leaf or gTass-feeders. Some are like 

 wolves in habits, others like marmots, weasels, squirrels, flying-squirrels, dormice or jer- 

 boas. All are members of one stock, and have no real affinity with the Old- World forms, 

 which they often outwardly resemble." Besides Marsupials, which are sometimes called 

 semi-oviparous, there are the still inferior Monotremes, the Duck-bill and Echidna, both 

 of which are strictly oviparous, although true Mammals inasmuch as they suckle their 



