698 GEOGRAPHICAL AND GEOLOGICAL BOTANY. 



In the northern zone beyond 60 N. lat., the species predominating 

 northwards are Graminacese, Cruciferae, Saxifragaceae, Caryophyllacese, 

 Ranunculaceae, Rosaceae, Cyperaceae (5-7 per cent.). Composite form 

 7 per cent, in Melville Island, but only 4-5 per cent, in Spitzbergeu. 

 Ainentiferae (Betulaceae, Salicaceae, &c.) and Juncaceae barely reach 5 

 per cent. ; Polygonaceae, Ericaceae, and Scrophulariaceae approach this 

 number, but are mostly below it. 



In the south temperate zone we find two classes of regions, one dry, the 

 other with a damp climate. The former comprehends the Cape of Good 

 Hope, Australia, Chili, and La Plata. Cornpositse predominate at the 

 Cape and in America, but in Australia fall to 7 per cent. Leguminosae, 

 on the contrary, make but 7 to 12 per cent, in America and at the Cape, 

 "but 14 per cent, in Australia. The Grasses are not more than 3 to 6 per 

 cent, anywhere, and the Cyperaceae still fewer. 



The Cape and Australia have, however, certain especially abundant 

 Orders ; thus Proteaceae form 2 to 6 per cent, at the Cape, 8-12 per cent, 

 in Australia ; Myrtaceae 9 per cent, and Epacridaceae 4-5 per cent, in 

 Australia; Iridaceae 4-6 per cent, Liliaceas 4-5 per cent., and Ericaceae 

 2-6 per cent, at the Cape ; Stylidiaceae and Goodeniaceae are especially 

 Australian. 



^ In the moist regions, comprising parts of the African coast, Tasmania, 

 New Zealand, Island of Chiloe, &c., the Grasses and Compositae increase iu 

 departing from the tropics ; Cyperaceae rise to 4-8 per cent, j Orchidaceae, 

 4|-8| per cent. ; and Ferns are very numerous in the islands. Restiaceae 

 increase in Tasmania, but Proteaceae, Leguminoseae, with Stylidiacese, 

 Goodeniaceae, &c. decrease. The proportions in the Southern extremity 

 of America approach those of the temperate and moist regions of the 

 northern hemisphere. 



As a general statement, it may be said that of the three most fre- 

 quently predominating Orders, Leguminosae are diminished in propor- 

 tion to temperature, the Compositae are lessened by combined cold and 

 humidity, and the Graminaceae are least predominant where the climate 

 is dry. 



It must be borne in mind that the above calculations are approximate 

 only, and apply to species, or genera, or orders, and by no means repre- 

 sent the distribution of individual plants. 



CHAPTER III. 



BOTANICAL GEOLOGY. 



Sect. 1. NATUEE AND IMPORTANCE or FOSSIL PLANTS. 



Remains and traces of plants are met with in most of the strati- 

 fied rocks which have been produced by successive geological 

 changes of the earth's surface. These remains afford an indica- 

 tion, more or less perfect in different cases, of the nature of the 



