179 



are distributed by birds, two by wind, and the other three have 

 edible pods or nuts. 



Linn Grove received its name from the presence of the Hnn 

 or basswood. It is situated on a high morainal hill, surrounded 

 by unusually rolling land, with thin or no prairie humus. It 

 probably owes its immunity from fire to the poverty of the 

 prairie vegetation. The trees in this grove are Tilia americana, 

 Ulmus americana, Ulmus fulva, Juglans nigra, Prunus serotina, 

 Carya cordiformis, Morus rubra, Gleditsia triacanthos, Gymno- 

 cladus dioica, Celtis occidentalis, and Crataegus sp. The similarity 

 of this list to the flora of Mink Grove is striking. Linn Grove 

 was for many years left practically untouched, although a few 

 trees were taken out for firewood. The undergrowth was of a 

 mesophytic climax type, with Asimina triloba and Cercis cana- 

 densis as the common shrubs, and a rich herbaceous flora with 

 such characteristic mesophytes as Trillium declinatum, Sangui- 

 naria canadensis, and Adiantum pedatum. 



The only explanation which can be offered for these two 

 groves is that seeds of certain forest trees were carried by birds 

 (or by Indians?) to these protected spots. With the development 

 of a forest cover, other species gradually immigrated, while the 

 relatively immobile oaks have never been able to cross the 

 intervening fire-swept prairies. 



III. The third general effect of prairie fires upon the forest 

 is seen in the generally narrower belt of forest along the western 

 side of streams. In some places the forest is completely limited 

 to the eastern side, in almost every case it is notably narrower, 

 and the widest strips of forest are invariably found where a bend 

 in the stream has afforded protection from both the west and 

 the south. Neither is this feature limited to central Illinois, 

 where the attention of the writer was first attracted to it. It 

 seems to be a common feature of the forests throughout Illinois 

 and eastern Iowa, at least, and is excellently shown by McGee 

 in his map of the forests and prairies of northeastern Iowa.* 



On the west side of streams running north or south, the forest 



* W J McGee, The Pleistocene History of Northeastern Iowa, U. S. Geol. 

 •Surv. Ann. Rep. ii, pt. i: lOO'Sll- I^I- 22. 1891. 



