176 



food for the next annual passage of the devouring element. 

 I have beheld many a line of ashes, marking the spot where the 

 entire trunk of a massy oak was consumed the previous autumn." 



The first invasion of forests into the Middle West was undoubt- 

 edly along the stream courses, where the more rapid erosion of 

 prairie humus, the looser prairie sod, and the protection from 

 excessive insolation and wind favored the germination of tree 

 seeds and the growth of the seedlings. The forests migrated 

 up the streams, following rather closely the valley and the 

 adjacent bluffs, usually as far as the effects of erosion were 

 obvious. They also migrated laterally from the valleys toward 

 the uplands, where they soon encountered the denser prairie sod, 

 which materially checked their further extension. The general 

 result of this forest invasion, as seen a century or more ago, 

 was the presence of a belt of forest along all the larger water 

 courses, varying in width with the size of the stream. 



It is not necessary to hazard an opinion as to the probable 

 date of the first prairie fire or its possible cause. It may be 

 stated that the writer has no record of a prairie fire produced 

 by lightning. If such a cause ever produced fires, they must have 

 been at widely separated intervals, and could have produced 

 no appreciable effect on the forests. But it is definitely known 

 that the Indians habitually started fires, and the prairie fire as a 

 phytogeographical factor dates back to the entrance of the Indian 

 or to the origin of this habit.* Since that time, the forests were 

 attacked practically every year on their western flanks by prairie 

 fires, and occasionally also on their eastern sides as well, unless 

 they were protected by some unusual feature of the topography 

 or by standing water. 



The effects of prairie fires from the east upon the forests are 



* One of the first statements to this effect was made by Hennepin (Voyage ou 

 nouvelle decouverte d'un tres-grand pays, dans I'Amerique enter le nouveau 

 Mexiqueet la mer glaciale, 1704, pp. 183, 184, 185), in describing his travels across 

 Illinois in 1679. " Ce ne sont que de grandes campagnes decouvertes, dans 

 lesquelles il ne croit que de grandes herbes, qui sont seches ordinairement dans la 

 saison, que nous y arrivames. Les Miamis les avoient brulees en chassant aux 

 boeufs ou taureaux sauvages." "lis y avoient mis le feu dans les herbes fanees 

 pour tuer plus facilement les taureaux & les vaches sauvages." "Les Sauvages 

 ayant mis le feu dans les herbes seches de toutes les preries de notre route." 



