CLASSIFICATION AND RELATIONSHIP 303 
31. thicket: lochmium 45. blowout: anemium 
b. Heliophytia: sun plant for- 40. strand: psamathium 
mations 47. dune: thinium 
32. meadow: poium 48. badlands: tirium 
33. pasture: nomium 49. hill, ridge: lophium 
34. culture land: agrium 50. cliff: cremnium 
35. waste place: chledium 51. rock field: phellium 
III. Xerophytia: dry plant forma- 52. boulder field: petrodium 
tions 53. rock, stone: petrium 
36. desert: eremium 54. humus marsh: oxodium 
37. sand-hills, sandy plain: 55. alkali area: drimium 
amathium 56. heath, dry meadow: 
38. prairie, plains: psilium xeropoium 
39. dry, open woodland: 57. moor: sterrhium 
hylodium 58. alpine meadow: cory- 
40. dry thicket: driodium phium 
41. dry forest: xerohylium 59. polar barrens: crymium 
42. gravel slide: chalicium 60. snow: chionium 
43. sandbar: syrtidium 61. wastes: chersium 
44. sand draw: enaulium 
Particular formations are indicated by means of floristic distinctions. 
Thus, Populus-hylium is the aspen forest as distinguished from the Picea- 
Pseudotsuga-hylium, or the balsam-spruce forest; and the Bulbilis-psilium, 
or buffalo-grass prairie, from the Bouteloua-Andropogon-psilium, or grama- 
bluestem prairie. Similarly, the aspen formation of the Old World and of 
the New may be distinguished as Populus-tremula-hylium and Populus- 
iremuloides-hyliuam, 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., (1) Populus-hylium (Crystal Park), (2) Populus-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 fotind 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 
