PRACTICAL STUDY OF PLANT FORMATIONS. 633 



Montane Districts. 



1. Valley series. 



2. Foothill series. 



3. Basal series. 



4. Montane series. 



5. (Alpine series beyond tree growth). 



In general physiographic divisions might be made similar to those given 

 in the table above for the more level districts, though modifications and 

 additions would be necessary when an actual survey of the district is made. 

 So in the following climatic regions a similar physiographic division might 

 be made, but some alterations and additions would be necessary because 

 of changed conditions of environment. For example, the oases in deserts 

 and plains, the warm oases, and the tundra in arctic regions, and so on. 



Prairie climatic region. ) 



_.. . .. . . > Grassland climatic region of Schimper. 



Plains climatic region, j 



Arctic climatic region. 



While the physiographic subdivisions of districts outlined above is only 

 suggested as a basis for an elementary practical study of vegetation of 

 local regions, the locality should be asssigned its proper place in some 

 one of the several plans proposed for the purpose of dividing the vegeta- 

 tion surface of the earth into large natural areas based either on physio- 

 graphic or climatic conditions or both. See Section II of this chapter. 



1122. Formations (= association of some students). Having looked over 

 the locality or district to be studied, and having prepared a chart showing 

 the distinct physiographic areas or edaphic areas to be examined in detail, 

 these principal formations can then be critically studied for the purpose 

 of determining the individual formation, or formations (= associations 

 of some students). 



1123. Dominant species in a formation. (i) Determine the different 

 formations with the one or more dominant species. 



(2) Chart its extent and limits in the locality or principal formation. 



(3) If there are evident layers (as in a forest or heath), determine the 

 prominent ones. 



(4) Where there is a slope providing a regular succession of series of 

 different soil conditions or water content, or a sloping shore and water 

 basin, determine the zones (or lateral layers) indicated by the different 

 individual formations down the sloping bank and gradually out into the 

 deep water. Even where topographic conditions are the same the ground 

 may be occupied by different species in different regions or at different 

 points along the same shore. All these peculiarities should be noted and 

 the formations of different lakes, ponds, etc., compared. For example, 

 in fig. 534 are shown several zonal formations. Beginning at the highest 



