THE PLANT WOKLD 187 



compelled to live. That this strain has not worked out even varietal 

 differences since the beginning of their isolation is very strange indeed. 

 The identity of each species has been placed beyond doubt by scrupu- 

 lous comparison with Eocky Mountain and Alpine specimens, and by 

 helpful conference with Euroj^ean students. In only one case is a 

 diversity of opinion to be recorded, and the circumstances justify a ref- 

 erence to it here. The noted Scandinavian brj^ologist, Dr. Kindberg, 

 dissents from the general judgment regarding Webera prollgera, and 

 considers it sufficiently different to stand as a distinct species. On all 

 the other plants the judgment is unanimous for perfect identity. 



One is naturally struck with the insular isolation in which these 

 plants exist in the midst of hundreds of strangers. Like Robinson 

 Crusoe on his island, they seem stranded on this area, living in it, 

 cramped climatically it may be, yet safely, as in a haven of refuge, since 

 they have ceased battling with the fiercer elements in the Ice Age. 

 This geological event seems to furnish the only satisfactory^ exi)lanation 

 for their existence together in this, to them, out-of-the-way corner of 

 the earth, for it may be stated, in closing this note, that the area on 

 which they occur is a part of the so-called Driftless Area, stretching 

 out as it were along its northwestern border. According to a letter 

 from Dr. F. W. Sardeson on this subject, the general boundary of this 

 Driftlees Area " might be given as from Winona, Minn., to Dubuque, 

 la., to Freeport, 111., to Madison, Wis., to Baraboo, to Black River 

 Falls, to Winona." Undoubtedly a closer study of the plants in this 

 large area, and more especially of the northern borders of it, in the 

 four states involved, will reveal other strangers as isolated as the above 

 seven plants; and when this survey is more complete than it is at pres- 

 ent, it is not unlikely that it will at least aid in answering some of the 

 puzzling questions regarding the physical and climatic conditions of 

 the Driftless Area in inter-glacial and early post-glacial time. 



Winona, Minnesota. 



