Gleason : Unsolved problems of the prairies 269 



Point may be compared with the presence of Cristatella Jamesii 

 and Lesqucrella argentca on the sand dunes along the Illinois and 

 Alississippi riv^ers, many miles from the nearest reported station in 

 Nebraska or Dakota, or of Opiintia fragilis in northwestern Illi- 

 nois. A number of insects found there have also a similar distri- 

 bution, as shown by Mr. C. A. Hart. Neither of the plants has 

 any means of dispersal adequate to bridge over this gap, and we 

 can only assume that at one time they had a distribution more 

 nearly continuous. What have been the causes which have re- 

 stricted them to these widely separated stations ? Is it possible 

 that there was a post-glacial period with so little rainfall that their 

 distribution was continuous over the whole desert-like intervening 

 territory ? And if so, what other Neo-Sonoran plants also reached 

 into Illinois at that time? Did we ever have Echmocereiis viridi- 

 Jlorus^ Cactus missowdensis, Cucurbita foetidisshna^ Yucca glaitca^ 

 or other plants of similar habits in this state ? 



The preceding questions have been phytogeographical in nature 

 rather than ecological and have to do mainly with the historical 

 development of the prairies. Following are some that relate more 

 directly to ecology : 



6. What was the structure of the original prairie associations? 

 The remnants of the prairie flora still existing along our railroad 

 tracks give only a faint idea of the normal structure of the prairie 

 vegetation. The older botanists neglected this matter almost en- 

 tirely, although it was open to direct observation. So far as I 

 know, but one botanist, C. W. Short, discusses the subject, in an 

 article published m 1845. He mentions particularly the aggrega- 

 tion of individuals of one species and contradicts the idea given 

 by popular, more impressionistic writers. "The flora of the 

 prairies, the theme of so much admiration to those who view them 

 with an ordinary eye, does not, when closely examined by the 

 botanist, present that deep interest and attraction which he has 

 been led to expect. Its leading feature is rather the unbounded 

 profusion with which a few species occur in certain localities than 

 the mixed variety of different species occurring everywhere.*' 

 Probably the time has passed when this question could have been 



E 



satisfactorily answered. 



7. Within every complex of related plant associations there 



