CLASSIFICATION AND RELATIONSHIP 



303 



31. thicket: lochmium 



b. Heliophytia: sun plant for- 

 mations 



32. meadow : poium 



33. pasture : nomium 



34. culture land: agrium 



35. waste place : chledium 

 III. Xcrophytia : dry plant forma- 

 tions 



36. desert: eremium 



37. sand-hills, sandy plain: 



amathium 



38. prairie, plains : psilium 



39. dry, open woodland : 



hylodium 



40. dry thicket: driodium 



41. dry forest: xerohylium 



42. gravel slide : chalicium 



43. sandbar: syrtidium 



44. sand draw : enaulium 



45. blowout : anemium 



46. strand : psamathium 



47. dune : thinium 



48. badlands : tirium 



49. hill, ridge : lophium 



50. cliff : cremnium 



51. rock field: phellium 



52. boulder field : petrodium 



53. rock, stone : petrium 



54. humus marsh : oxodium 



55. alkali area: drimium 



56. heath, dry meadow : 



xeropoium 



57. moor : sterrhium 



58. alpine meadow : cory- 



phium 



59. polar barrens : crymium 



60. snow : chionium 



61. wastes: chersium 



Particular formations are indicated by means of floristic distinctions. 

 Thus, Poptilus-hyliiim is the aspen forest as distinguished from the Picea- 

 Pseadotsuga-hylium, or the balsam-spruce forest; and the Bulb His- psilium, 

 or buffalo-grass prairie, from the Boutelona-Andropogon-psiliiiin, or grama- 

 bluestem prairie. Similarly, the aspen formation of the Old World and of 

 the New may be distinguished as Popnlus-trcnmla-hylium and Popiilus- 

 iremidoides-hyliurn, respectively. In all formational names, the facies alone 

 should be used. Frequently, a single facies will suffice for clearness. As a 

 rule, however, the two most important facies should be employed; in rare 

 cases only is it necessary to use the names of three. When it is desirable to 

 refer to two or more examples of the same formation, a geographical term is 

 added, e. g., (i) Populus-hylium {Crystal Park), (2) Populns-hylium 

 (Cabin Canyon). 



353. Developmental classification. This is based upon succession as the 

 record of development. Upon the basis of development, all the formations 

 which belong to the same succession are classed together. They are ar- 

 ranged within each group in the sequence found in the particular succession. 

 From its nature, developmental classification is of primary importance in 

 exhibiting the history of vegetational changes. It has less value than the 



