193 



Prunus pumila, representing the endemic element along the 

 lake. 



A comparison with the flora of the sand-hills of Nebraska, 

 on the other hand, shows some striking similarities. Rydberg 

 ('95) lists 35 species as characteristic of the sand-hill region, 

 and of these, 15. or nearly one half, grow also in the central- 

 Illinois sand region, and this includes a number of the most 

 abundant species. Of the 188 species enumerated in this paper, 

 75, or 40 percent, are included also in Rydberg's list. 



It is evident from the preceding paragraphs that as a whole 

 the flora is essentially western in its relationships. Its position 

 within the Prairie province, as defined by Pound and Clements, 

 can not be questioned, and the region may well be regarded as 

 an isolated portion of the sand-hill division of the Prairie prov- 

 ince, formed under peculiar conditions, but closely resembling 

 the main body in its ecology and vegetation. The species found 

 only in the black-jack oak forest are almost entirely eastern in 

 their distribution, and have usually a wide range through the 

 state in different plant associations. 



Of especial interest from a phytogeographical standpoint 

 are Cristatella Jamesii and Lesquerella spathulata. This is 

 the first report of their occurrence in Illinois, and, so far 

 as known, at any station east of central Nebraska. The form- 

 er ranges through the sand-hill region from Nebraska south 

 into Texas, and according to Britton's Manual into Louisiana. 

 In Nebraska it lives in almost precisely the same conditions as 

 in this state; that is, in the bottoms of blowouts, where there 

 is a comparatively rapid shifting of the sand In 1903 it was 

 found in but a single blowout near Havana, and the total num- 

 ber of individuals was probably less than five hundred. In 1904 

 it had spread to two other blowouts in the same field, and it 

 was also found in great profusion in a large blowout about 

 ten miles northeast of Havana. Lesquerella spathulata, de- 

 scribed in 1896 from the Black Hills, ranges, according to 

 Britton, from Nebraska to Montana and the Northwest Terri- 

 tory. Rydberg's original plants ('96) grew on dry hilltops, a 

 habitat paralleled by its growth in Illinois in the bunch-grass 



