"344 ALTERNATE GLACIAL TEKIODS Chap. XI. 



mention still more ancient formations. But in relation to our 

 present subject, the most important result arrived at by Mr, 

 Croll is, that whenever the northern hemisphere passes through 

 a cold period, the temperature of the southern hemisphere is 

 actually raisctl, with the winters rendered much milder, chiefly 

 through changes in the direction of the ocean-currents. So, 

 conversely, it is with the northern hemisphere, when the south- 

 ern passes through a glacial period. These conclusions have, 

 as we shall immediately see, a most important bearing on geo- 

 graphical distribution ; but I will first give the facts which de- 

 mand an explanation. 



In South America, Dr. Hooker has shown that, besides many 

 closely-allied species, between forty and fifty of the flowering 

 plants of Terra del Fuego, forming no inconsiderable part of 

 its scanty flora, are common to North America and Europe, 

 enormously remote as these areas in opposite hemispheres are 

 from each other. On the lofty mountains of equatorial America 

 a host of peculiar species belonging to European genera occur. 

 On the Organ Mountains of Brazil, some few temperate Euro- 

 pean, some Antarctic, and some Andean genera were found 

 by Gardner, which do not exist in the low intervening hot 

 countries. On the Silla of Caraccas the illustrious Humboldt 

 long ago found species belonging to genera characteristic of 

 the Cordillera. 



In Africa, several forms characteristic of Europe and some 

 few representatives of the flora of the Cape of Good Hope oc- 

 cur on the Mountains of Abj'ssinia. At the Cape of Good 

 Hope a very few European species, believed not to have been 

 introduced by man, and on the mountains several representa- 

 tive European forms are found, which have not been discovered 

 in the intertrojDical parts of Africa. Dr. Hooker has also lately 

 shown that several of the plants living on the upper parts of 

 the lofty island of Fernando Po and on the neighboring Cam- 

 eroon Mountains, in the Gulf of Guinea, are closely related to 

 those on the Mountains of Abyssinia, and likewise to those of 

 Icinperate P^urope. It now also appears, as I hear froni Dr. 

 Hooker, tliat some of these same temperate plants have been 

 discovered by the R;'v. R. T. Lowe on the mountains of the 

 Cape de V^erde Islands. This extension of the same temperate 

 forms, almost under the equator, across the whole continent of 

 Africa and to the mountains of the Cape de Verde archipelago, 

 is one of the most astonishing facts ever recorded in the dis' 

 tribution of plants. 



