18 FLORA OF MICHIGAN. 



feet high; one small ash, two elms, two poplars, one beech, which grows 

 very large but not very high; one small white birch, one species of pine, by 

 no means a match for our white pine; a species of oak which sometimes 

 grows to a great size. 



Great Britain has about ten species of trees native to her soil. Michigan, 

 with half the territory, has sixty-nine species (ninety if we compare the 

 sizes exactly), nine times as great a variety. Great Britain has no white- 

 wood, no white or red cedar, no walnuts or hickories. Michigan has six 

 species of maple of tree size, a basswood, a whitewood, honey locust, 

 Kentucky coffee tree, three cherries, a pepperidge, five species of ash, a 

 sassafras, three elms, a hackberry, a mulberry, a buttonwood, black walnut, 

 butternut, six hickories, ten oaks, a chestnut, a beech, four tree birches, 

 four willows of tree size, five poplars, three pines, two spruces, one hem- 

 lock, a balsam fir, one larch, one arbor-vitse and a red cedar. 



The forests of North America may be divided into two regions, the 

 Atlantic and the Pacific. In the Atlantic region there are 292 species, in 

 the Pacific region 153 species. 



In all Europe there are only 85 species of trees. 



WHY HAS MICHIGAN SO MANY TREES AND GREAT BRITAIN SO FEW. 



This question now very naturally arises: Why has the Atlantic region, 

 including Michigan, so many species of trees and why has Europe so few? 

 Certainly we cannot attribute this difference to a defective soil and climate 

 of Europe, as they now exist, for Europe can grow all sorts of trees now 

 found in the temperate zone, while " Great Britain alone can grow double 

 or treble the number of trees that the Atlantic States can." 



The former geological conditions of their continents help to explain all 

 this difference in the distribution of trees to the entire satisfaction of 

 scientists. 



Away back in the Tertiary Period the trees of the regions now possess- 

 ing an arctic climate were such as now thrive in a warm temperate zone 

 like that of Georgia and California. This is well illustrated by the 

 abundant fossil remains of trees. Following this, came a long time when 

 extreme cold prevailed, known as the Glacial Epoch, when snow and ice 

 for niost or all of the year extended to the Ohio river. At the approach of 

 cold, the trees slowly retreated southward, as generation followed genera- 

 tion. The plants such as now thrive in southern Michigan, perhaps then 

 extended to what now forms the State of Alabama, while the arctic plants 

 reached Ohio. 



As the climate again gradually grew warmer, the trees and other plants 

 slowly migrated northward. Some arctic plants were stranded on the 

 White mountains and in Labrador, where they still remain; others went 

 farther north. 



Plants of the cool temperate zone reached Michigan. In a similar manner, 

 during the Glacial Epoch the plants of Europe were driven southward. 

 The Alps, the Pyrenees, the Appenines, the Caucasus, still contain some 

 of these arctic plants which retreated there at the close of the Glacial 

 Epoch. Most of the plants of the warm temperate region had perished 

 and therefore were unable to retreat when the continent became warmer. 



I quote the words of Dr. A. Gray, from whom other hints are taken, as 

 found in the American Journal of Science, page 194, 1878. " I conceive 

 that three things have conspired to this loss. First, Europe hardly extend- 



