270 THE FORMATION 



II. Anomalous successions : xenodochae i$voj, strange, unusual) 



327. illustrations. The following series will illustrate the application of 

 this system of nomenclature to particular successions, and their stages, or 

 formations. 



Thlaspi-Picea-sphyrinm : pennycress-spruce talus succession 

 Thlaspi-Eriogonum-chahcium : peimycress-eriogonum Igravel slide forma- 

 tion. 

 Elymus-Gilia-chalicium : wildrye-gilia half gravel slide formation 

 Quercus-Holodiscus-driodium : oak-fringewood dry thicket formation. 

 Pinus-xerohylium : pine dry forest formation 

 Picea-Pscudotsuga-hylium : spruce-balsam forest formation 



Bryum-Picea-pyrium : moss-spruce bum succession 

 Bryum-telmatium : moss meadow formation 

 Aster-Chamaenerium-poium : aster- fire weed meadow formation 

 Deschampsia-Carex-poium : hairgrass-sedge meadow formation 

 Salix-Betula-helodrium : willow-birch meadow thicket formation 

 Populus-hylium : aspen forest formation 

 Picea-hylium : spruce forest formation 



Lecanora-Carex-hedium : lichen-carcx residuary succession 

 Lecanora-Gyrophora-petrium : crustose lichen rock fomiation 

 Parmelia-Cetraria-chalicium : foliose lichen gravel slide formation 

 Paronychia-Silene-chalicium : nailwort-campion gravel slide formation 

 Carex-Campanula-coryphium ! sedge-bluebell alpine meadow formation 



Eragrostis-Helianthus-xcrasium : cragrostis-sunflower drainage succession 

 Eragrostis-Polygonum-telmatium : eragrostis-heartsease wet meadow for- 

 mation 

 Helianthus-Ambrosia-chledium : sunflower-ragweed waste formation 



INVE8TIQATI0N Of SUCCESSION 



328. Generai rules. The study of succession must proceed along two 

 fundamental lines of inquiry: it is necessary to investigate quantitatively 

 the physical factors of the initial stages and the reactions produced by the 

 subsequent stages. This should be done by automatic instruments for 

 humidity, light, temperature, and wind, in order that a continuous record 

 may be obtained. Water-content is taken daily or even less frequently, while 

 soil properties, and physiographic factors, altitude, slope, surface, and ex- 

 posure arc determined once for all. It is equally needful to determine the 

 development and structure of each stage with particular reference to the 

 adjacent formations, to the stage that has just preceded, and the one that is 



