372 



Liriodendron tulipifera. 



Acer sncchariiiuiii. 

 Acer nibrum. 

 Praxinus nigra. 

 Fraxinus americana. 

 •luglans einera. 

 Ulmus americana. 

 Ulmus raeemosa. 

 Platanus occidental is. 

 Lindera benzoin. 

 Xanthoxylum americanum. 

 Pi lea pumila. 

 Urticastrum sp. 

 Thalictrum dasycarpum. 



We have in the cedar swamp a formation of plants of a decidedly boreal 

 aspect, maintaining itself, but for the influence of man, in the midst of a 

 flora predominantly southern. Ability to maintain itself in the struggle with 

 the southern flora was probably due originally to differences in the habitat. 

 Just what the factors are that make bog conditions unsuitable for the growth 

 of most plants have not been fully determined; but some combination of 

 edaphic conditions permitted the northern plants to remain and removed 

 them very largely from competition with the southern forms. In the later 

 stages of the development of the bog, many of these conditions have probably 

 been modified or removed. Many of the southern plants could undoubtedly 

 maintain themselves under the present conditions; but the bog plants have 

 such complete possession of the habitat that invasion is practically pre- 

 cluded. But for the influence of man, the formation would no doubt have 

 been able to maintain itself for many centuries to come. 



About two miles southeast of Richmond, Ind., lies a small remnant of 

 a formerly much more extensive peat bog. It is known as the Elliott's Mills 

 bog and is in such an advanced state in the physiographic cycle of bogs that 

 little resemblance to a typical bog remains. But the characteristic peat 

 soil and the presence of certain bog and boreal plants indicate its former 

 character. The bog lies in a broad, shallow valley between morainic hills. 

 It evidently occupies a shallow, undrained depression scooped out in a softer 

 part of the underlying Niagara limestone. The bog is crossed by a public 



