26 Forestry Quarterly 



position of the plant societies, and their record by cartographic, 

 photographic and herbaria method are described. Among the 

 different kinds of plant associations, making a difference between 

 aggregation and association, the forest receives special attention 

 under " light association." The development of associations 

 by invasion and succession, the kinds and causes of zonation 

 (zonal distribution), and the disturbing elements, or causes and 

 kinds of alternation, producing differentiation within the zones 

 are all subjects intensely interesting even to the practicing 

 forester. Various forest types, and their changes or successions, 

 as in burned and lumbered areas, are adduced in explanation. 



Still adhering to temperature as a basis for classification (see 

 Forest Centers on p. 38 of this number), the following zones and 

 provinces are recognized for the North American vegetation. 



I. Polar-niveal zone. Nebraska province, 



II. Artic-alpine zone, Utah province, 



Artie province. Coast province, 



Alpine province. Pacific province. 



III. Boreal- sub alpine zone, V. Subtropical zone, 



Alaska province, Florida province, 



Cordilleran province, Mexican province. 



Ontario province. VI. Tropical zone, 



IV. Temperate zone, Antilles province, 



Atlantic province, Andean province. 

 Appalachian province, 



To establish a uniform nomenclature, a number of lists are 

 inserted. A. list of sixty one formations, for instance, is given, 

 their names, vernacular and scientific, being based on the habi- 

 tat which they occupy, classified into hydrophytia : water plant 

 formations ; mesophytia : middle plant formations ; xerophytia : 

 dry plant formations. The forest formations, cited in this list, are : 

 swamp forest (helohylium); swamp open woodland (helodium) 

 for the first class ; the mesophytic forests (hjdium) ; grove (al- 

 sium) ; open woodland (orgadium) ; thicket (lochmium) ; the 

 xerophytic open woodland (hylodium) ; dry thicket' (driodium) ; 

 dry forest (xerohylium). Particular formations then are indi- 

 cated by means of floristic distinctions, like Picea-Pseudotsuga- 

 hylium, Pinus- xerohylium, Populus- Picea-mictium (transition 

 stage to Picea-hyliuni) . 



