870 



SCIENCE. 



[N. S. Vol. XII. No. 310. 



logical frequency curves, and their change 

 •with changing place and environment. 

 The idea of correlation has received a pre- 

 cise definition. The results of experimen- 

 tation have been quantitatively expressed. 

 The role of natural selection, the method 

 of evolution and the laws of inheritance 

 are being discovered. Already we are able 

 to predict greater results from the quanti- 

 tative method in biology, especially where 

 combined with experimentation, than any 

 •which have yet appeared. 



Chas. B. Davenport. 

 Univeesity or Chicago. 



PLANT GEOQBAPHY OF NORTH A3IEBICA. 

 COMPOSITION OP THE ROOKY MOUNTAIN FLORA. 



In Southern Wyoming the Great Plains 

 extend across the continental divide, mak- 

 ing a break in the Rocky Mountain chain, 

 and dividing it into two groups, the South- 

 ern and the Northern Eockies. The former 

 are for the greater part in the State of Colo- 

 rado, but extend into northern New Mexico 

 as -well as southern Wyoming. The Wa- 

 satch and Uintah Mountains, although sep- 

 arated from the main claim by the Grreen 

 River Basin, may also be noted here.* 



The Northern Rockies begin in northern 

 Wyoming, but have their best development 

 in western Montana, northern Idaho, west- 

 ern Alberta and eastern British Columbia. 

 The chain also extends into Alaska and 

 Yukon Territory, but the flora of this re- 

 gion is partly very little known and so 

 merged into the Pacific Coast flora that it 

 deserves a separate treatment. Some iso- 

 lated mountains, as for instance the Black 

 Hills of South Dakota and the Little Rockies 

 and Bear Paw Mountains of Montana, may 

 also be mentioned here. 



■*The motmtains of southern New Mexico and 

 Arizona may also be accounted to the Rocky Mountain 

 system, but their flora is so different and contains so 

 many Mexican and Sonoran elements that it is better 

 to exclude them from this discussion. 



The flora of the two groups is essentially 

 the same, but some differences are found. 

 These are most evident in the coniferous 

 vegetation. So are for instance Pinus edulis, 

 Pinus aridata, Picea Parryana and Abies eon- 

 eolor confined to the Southern Rockies, while 

 Pinus Murrayana, Picea Columbiana and Abies 

 grandis take their place in the Northern. 

 Psudotsuga mueronata, Picea Engelmannii and 

 Pinus fiexilis are equally common in both re- 

 gions. 



The flora of the mountain regions is made 

 up of the following elements : 



1. The Endemic Flora of the Rookies, 

 which constitutes the largest element. In 

 Montana it is represented by 33 per cent, of 

 all the species and in the Southern Rockies 

 the proportion is much larger. 



2. The Transcontinental Flora, made 

 up mostly of hydrophilous plants. 



3. The Boreal Flora of North Amer- 

 ica, which in British America is more or 

 less transcontinental, but in the United 

 States is found principally in the mountain 

 regions. It is made up mostly of hyloph- 

 ilous plants, but also represented by some 

 hydrophilous ones, as for instance members 

 of Cyperaceie, Salicaceoe and EricacecR. 



4. The Arotio Flora, found only on the 

 tops of the highest peaks at an altitude of 

 over 3,000 m. in Montana and over 4,000 m. 

 in southern Colorado. 



5. The Cascade Mountain Flora, which 

 merges with that of the Rockies in British 

 Columbia and partly extends south into 

 Montana and Idaho. 



But in discussing the flora of the Rockies, 

 one must not only take in consideration 

 that of the mountain regions, but also that 

 of the intermingling plains, valleys and foot- 

 hills. If this is done, several new elements 

 must also be considered. 



6. The Flora op the Great Plains. 

 The Great Plains consist of high dry table- 

 lands and make up a large portion of Sas- 

 katchewan, Assiniboia, eastern Montana 



