127 



flora. The origin of the prairies has been referred to the char- 

 acter of the soil, the distribution and amount of rainfall, the 

 direction of the prev^ailing winds, the grazing of bison and to 

 forest fires. Each of these has probably had some influence in 

 accelerating or retarding the inv^asion of the prairie or forest after 

 the retreat of the continental ice-sheet, but the most important 

 factor of all is historical rather than physical in nature. At the 

 close of the glacial period the territory since occupied by prairies 

 was opened first to invasion from the southwest, a region of 

 climatic prairies, and subsequently to invasion from the climatic 

 forests of the southeast. The two floras, on meeting, adjusted 

 themselves to each other and to the physical factors of the en- 

 vironment, so that the forests occupied the bluffs and valleys 

 along the streams, and the prairies the high lands between them. 

 The climate and soil were adapted to the growth of the forest, so 

 that, until extensive cultivation was begun, the prairie was gradu- 

 ally being displaced. 



A comparatively restricted area along the Illinois River is occu- 

 pied by sand deposits covered with a vegetation essentially similar 

 to that of the sand-hill region of Nebraska, and entirely different 

 from that of the dunes at the head of Lake Michigan. 



After an interesting discussion of Mr. Gleason's paper. Dr. 

 Rusby exhibited various plants used as food by the Indians. 

 Among these were young shoots of the cat-tail, specimens of 

 bitter-root used by the Indians of the northwest, and kouse^ 

 which consists of several species of Lomatiinn [L. Canbyi, and 

 L. Koiis) and is an important article of Indian diet. Dr. Rusby 

 spoke also of the use by the Indians of the young buds of the 

 beech tree, which are edible, when cooked, at any date after the 

 first of January. 



Dr. N. L. Britton exhibited fruits of the palm Acrocomia media 

 Cook, recently collected by him in Porto Rico, and remarked on 

 the relationships and distribution of this species, referring to the 

 fine specimen of the plant growing in the palm collections of the 

 Garden, brought by Mr. Percy Wilson from that island several 

 years ago. He stated that his observations on this tree showed 

 that the trunk does not invariably bulge above the base, as 



