March 7, 1913] 



SCIENCE 



377 



underlying rocks of the Arikaree formation with 

 a loose porous soil varying in depth from a few 

 feet to over 150 feet. Wind action is still a pro- 

 nounced factor in shaping the topography of the 

 uplands, although the region as a whole is prac- 

 tically stabilized by invading vegetation. The 

 influence of wind is reflected most forcibly at 

 present in the regions of active "blow-outs'' and 

 "sand-draws." 



The greater part of the upland in this great 

 dune region is effectively held against wind ero- 

 sion by the Bunch-grass Association, a sub-division 

 of the Prairie Grass Formation. Another con- 

 spicuous association of the upland is the Blow-out 

 Association. The valleys are characterized by 

 less serophilous association which in the main are 

 members of the Prairie Grass Formation to the 

 east. The Short Grass Formation has pushed in 

 from the west in a number of places and has 

 occupied especially the hard land in some of the 

 valleys. Forest formations are found along 

 streams and spring branches that are related to 

 the central hardwoods region and to the Rocky 

 Mountain forest region. The streams, wet valleys 

 and numerous lakes reveal the presence of a num- 

 ber of marsh and aquatic associations which are 

 in the main similar to such associations found 

 farther eastward in the Prairie Grass Formation. 



The International PhytogeograpJiic Excursion of 

 1911 and 1913: H. C. Cowles, University of 



In August, 1911, there was held in the British 

 Isles under the auspices of the British Vegetation 

 Committee the first International Phytogeographic 

 Excursion. A dozen phytogeographers from six 

 different countries were conducted to the places in 

 England, Scotland and Ireland where the natural 

 vegetation is of greatest interest. In all the places 

 visited there were competent British guides, who 

 were very familiar with the vegetational features 

 to be considered. The guiding spirit of the excur- 

 sion was Dr. A. G. Tansley, of Cambridge, who 

 accompanied the party throughout the tour, and 

 attended to numberless details. 



Among the many valuable features of the Brit- 

 ish excursion were (1) the opportunity of getting 

 intimately acquainted in a short time with the 

 most important features of the British vegetation; 

 (2) the opportunity to know in intimate fashion 

 the British botanists who accompanied the party 

 and who were met from place to place, and to 

 know with special intimacy the foreign colleagues 

 with whom we were associated closely every day 



for a month; (3) the opportunity to discuss the 

 problems of vegetation as we met them together 

 in the field, and thus without misunderstanding 

 one another and with the certainty that we were 

 talking about the same things. 



It was the unanimous opinion of those who par- 

 ticipated in the British excursion that the benefits 

 to all were so considerable that similar excursions 

 should be made a permanent feature of Interna- 

 tional Phytogeography, and at frequent intervals. 

 The second excursion has been definitely an- 

 nounced for the United States in August and 

 September, 1913, and it has been suggested that a 

 third excursion be held on the continent of Europe, 

 immediately after the conclusion of the London 

 Botanical Congress in 1915. It is hoped that 

 American botanists, and especially those inter- 

 ested in the advance of ecology and plant geog- 

 raphy, will cooperate in every way possible to 

 make the excursion of 1913 a great success. 



Prairie Openings in a Forest Region: B. Shimek, 



Iowa State University. 



A prairie opening on the exposed terminus of 

 a ridge near Iowa City, Iowa, has retained its 

 original prairie flora through all the changes inci- 

 dent to the clearing of much of the surrounding 

 country and the building of an electric railway 

 which cuts a part of the ridge. 



The distinction between the flora of this area 

 and an adjoining timbered tract is sharply brought 

 out by comparative lists of the plants. The plants 

 of the latter area are broad-leaved, and the leaves 

 present a distinct dorsi-ventral structure, while 

 those of the prairie are narrow-leaved, and the 

 leaves are often more nearly erect or ascending. 



A comparison of evaporation and transpiration 

 on the two areas shows that evaporation is much 

 greater on the open surface, but that transpira- 

 tion may be less. 



An artificial opening, created by a road-clearing 

 through the original forest near Homestead, Iowa, 

 more than fifty years ago, is similarly discussed 

 with reference to its flora. The greater part of 

 the area is somewhat sandy, and the road-strip, 

 which is about fifty feet wide, extends almost due 

 north and south through about a mile of forest. 



This roadway has been kept clear of larger 

 brush and small trees which occasionally spring 

 up, and as a result a very characteristic prairie 

 flora has taken possession of most of the roadside. 



Both areas are discussed with reference to their 

 bearing on the question of the causes of the tree- 

 lessness of the prairies, and the fact is emphasized 



