151 



An external factor, strangely enough, almost entirely pre- 

 cludes the determination of a peculiar herbaceous flora for this 

 association, viz: that owing to the enormous production of 

 very nutritious acorn food, such groves are almost invariably 

 "hog pastures," and all wild growth has either become exter- 

 minated, or so mixed with pasture weeds as to become useless 

 for purposes of study. 



Above this growth on all the lands lying adjacent to the 

 great Niagara mounds, so common and conspicuous a feature 

 of the landscape of northwestern Illinois, is to be found an ir- 

 regular belt or zone, occupied largely by black walnut and red elm, 

 w'hich here and there, by reason of the erosion caused by some 

 drainage line, assumes the form of a great amphitheater, sur- 

 rounded on all sides, but the outflowing, by the steep slopes of 

 the mound, partly Cincinnati and partly Niagara, both talus- 

 like in appearance. In such places the species named reach 

 magnificent proportions, are very numerous in individuals, and 

 are commonly associated with basswood and red oak in much 

 less numbers. The soil is very rich, full of humus, plentifully 

 supplied with moisture, and is by all odds the most prolific in 

 species of any area in the entire region. Here are to be found 

 in great profusion those species that are the rarest of plants 

 elsewhere. 



Nowhere except in the immediate valley of the Mississippi 

 river are the trees so luxuriant. The undergrowth resembles 

 in most particulars the rich scarlet oak type of the first as- 

 sociation and many of the herbaceous plants are the same. 

 From this it would seem that shallow-rooted plants find the 

 areas quite similar, but the deep-rooted trees evidently discover 

 something in the one region not found in the other, and this 

 something is potent enough to produce a great difference in 

 tree growth. 



In these favored ampitheaters are to be found, among others, 

 the following herbaceous plants various rare Carices as C. 

 albursina, pedunculata, plantaginea, Frankii, Erythronium alhi- 

 diim by thousands, Uvidaria grandifiora, Orchis spectabilis, 

 Asarum canadense Actaea rubra, Sanguinaria, Dicentra cucul- 



