The bur oak is the dominant forest type in all these border 

 portions of the groves. Although in various parts of the state 

 this species shows a remarkable power of adaptation to different 

 conditions, in this region it is essentially a xerophyte, of a more 

 or less stunted type, extreme border specimens being sometimes 

 reduced almost to the minimum western form which has received 

 the name Quercus macrocarpa var. dep7^essa with, rough, very 

 corky, irregular t^vigs, and reduced leaves and acorns. Occa- 

 sionalty Fraxiniis pennsylvanica var. lanceolata^ some species 

 of Craiagus, and Prunus americana occur with the bur oaks. 

 Mingled with these border trees a shrub, Sympkoricarpos occi- 

 dentalis is usually quite common. 



The herbaceous plants of these open borders are partly those 

 of the prairie, as is shown in columns VII and VIII of the pre- 

 ceding list, and partly forest mesophytes which usually persist 

 in more sheltered nooks and minor depressions. This mixing of 

 forest and prairie floras is clearly due to the blending of the 

 physical conditions which prevail in each type. 



Mingled with the prairie species of columns VII and VIII in 

 the open forest borders are certain species which are listed in 

 this paper with the forest plants, but which are most frequent 

 on the border areas. Such are the following : 

 Apocynum androsaemifolium Prunus virginiana 

 Clematis virginiana Prunus americana 



Celastrus scandens Quercus macrocarpa 



Crateegus macracantha Rudbeckia triloba 



Crataegus mollis Rosa blanda 



Crat«gus punctata Rhus glabra 



Crataegus sp. ? * Ribes floridum 



Erysimum cheiranthoides Zanthoxyllum americanum 



Helianthus Isetiflorus Viburnum lentago 



Of the forest plants proper the follo^^ang were found most fre- 

 quently in the border areas: 



* Acer negundo Oryzopsis racemosa 



10 This form has been reported by the writer in several papers as Quercus ma- 

 crocarpa var. olivaeformis, which is incorrect. The form was first named Q. obtusiloba 

 var. depressa by Xuttall in "The Genera of North American Plants," 1818, vol. II, p. 

 215, and was later referred to macrocarpa by Englemann in "The Oaks of The United 

 States," in the Transactions of the Academy of Science of St. Louis, vol. Ill, 1876, 

 p. 111. The name should therefore be wi-itten Quercus macrocarpa var. d-epressa 

 (Xutt. ) Eng. The form is clearly an ecological variety which grades into the type, 

 but it is convenient to retain the name for ecological discussions. 



39 



