1921] PALMER, BOTANICAL RECONNAISSANCE OF SOUTHERN ILLINOIS U9 



trifoli 



Mound 



mation and also along moist rocky bluffs in the Ozark region. 



Acer saccharum L, In forests of the Mounds Formation this species 

 is in places one of the commonest and largest trees; and in the Ozark 

 Ridge it occurs frequently along rocky bluffs and in rich, well-drained 



soil along small streams. 



Acer saccharum var. Rugeli (Pax) Rehd. Occasionally found with 



the species in the Mounds Formation and northward. 



Acer saccharum var. Schneckii Rehd. This variety is often the com- 

 monest Sugar Maple in the Mounds Formation; and it is also less abun- 

 dantly in the higher bottoms of the Cairo Formation and in alluvial 

 ground in the Ozark Ridge. It appears to be restricted to the central 

 Mississippi Valley, ranging through western Tennessee and Kentucky, 

 where it is comparatively rare, and through southern Illinois, south- 

 eastern Missouri and northeastern Arkansas, reaching its greatest de- 

 velopment in southern Illinois. 



Acer nigrum Michx. f. Noted only in Johnson County, in rich alluvial 

 land along a small stream, where a number of large-sized trees were grow- 

 ing, associated with A, saccharum and its variety Rugeli. 



Acer saccharinum L. Often abundant in low woods and on alluvial 

 banks of streams. Commonest in the Cairo Formation. 



Acer ruhrum L. Occurs more or less commonly throughout the region. 

 In the Cairo Formation trees of this species often attain a large size in 

 the swamps and low woods; it is also frequent along streams in the Mounds 

 Formation. In the Ozark Ridge a form sometimes is found growing 

 on dry rocky bluffs and hillsides, of quite different habit and appear- 

 ance. This form, which is common on the rocky bluffs and hillsides of 

 the Ozark plateau in Missouri and Arkansas, is often shrubby, with pale 

 mottled smooth bark and nearly glabrous foliage. 



Acer ruhrum var. tridens Wood. In the Ozark Ridge region and north- 

 ward this is a rather common form, and in places even more abundant 

 than the typical form of the species. 



Acer ruhrum var, Drumviondii (H. & A.) Sarg. Common in swamps 

 of the Cairo Formation, and extending up the Wabash Valley at least 

 as far as Richland and Wabash Counties. 



Acer Negundo L. Found throughout the region in low woods and 

 along streams. Most abundant in the Cairo Formation. 



Aesculus glabra Willd. Seen only In low rich bottoms of the upper 

 Cache River, near Tunnel Hill and Vienna, Johnson County, where it 

 becomes a tree with a maximum height of 10 or 12 metres. 



Aesculus oclandra Marsh. A few small shrubby specimens were found 

 on a rocky hillside above the Ohio River, near Golconda, Pope County. 



Rhamnus caroliniana Walt. Seen only along low rocky bluffs, in the 

 Gold Hills, near Shawneetown, Gallatin County. 



Ceanothus americanus L. Observed only in the Ozark Ridge region, 



in dry rocky open woods. 



