proceedings: philosophical society 141 



cultivated species, such as Trifolium repens, for example, like a great 

 many other Leguminosae, was extremely sensitive to acid or sour soils. 

 Many such plants can exist only for a couple of seasons in a soil requir- 

 ing more than 6000 pounds of lime per acre foot, that is, to a depth of 

 one foot. On the other hand, some forage species, notably Agrostis 

 alba, as evinced by the luxuriant growth made, prefer sour soils. Thus, 

 in a judicious reseeding of the native depleted grazing lands, a study of 

 the native plant societies, as indicators of acid alkalinity or neutrality 

 of the soil, is imperative. 



In general, strongly acid habitats are characterized by a superabun- 

 dant supply of moisture coupled with poor drainage. Locally, such 

 lands usually support dense stands of vegetation, such as Carex, which 

 often produce a matted surface and an entanglement of long root stalks 

 which bind the soil firmly. 



When this study was first undertaken, it was presumed that the latter 

 soils — those with an intricate mass of interwoven roots and having an 

 air dry weight of 15 pounds per cubic foot, were the more acid. Later, 

 however, it was found that the sour soils are those of the well-drained 

 lands which support the mountain bunchgrass (Festuca viridula) society. 

 The soils upon which this society occurs vary in lime requirements for 

 neutrality from 5000 pounds as a minimum to 41,000 pounds as a maxi- 

 mum. Such habitats are found to be acid to a depth of about five feet. 

 The greatest lime requirements for neutrality occur in the superficial 

 layer. 



The acid endurance and requirements of the various local conspicuous 

 plant societies follows : They are arranged in accordance with the de- 

 gree of acidity of the substratum. 



(1) Festuca viridula society, (2) Carex society, (3) Alnus-Salix 

 society, (4) Veratrum-Rudbeckia-Mertensia-Valeriana society, (5) 

 Phleum-Elephantella-Dodocatheon society, (6) Vaccinium-Phyllodoce 

 society, (7) Deschampsia-Juncoides society, (8) Pinus-Calamagrostis 

 society, (9) Pinus-Abies-Polemonium society, (10) Panicularia-Cinna 

 society. 



The mountain bunchgrass {Festuca viridula) society, as stated, has 

 the most acid soil. It occurs throughout the extensive well-drained 

 meadows, and bald buttes of the Hudsonian zone on the characteristic 

 basaltic clay loam soils. 



While the genera that make up these associations are mainly confined 

 to sour soils, some species seem to show no particular preference for 

 acid lands, or at least they occur abundantly alike on sour, neutral, and 

 alkaline soils. The most important genera that inhabit the calcareous 

 rock formations are: Pteridium, Aquilegia, Achillea, Pentstemon, 

 Lupinus, Erigeron, Agropyron, Elymus, Sitanion, Stipa, Berberis, 

 Artemisia, and Populus. Of these it is definitely known that Pteridium, 

 Lupinus, Stipa, and Populus occur also on somewhat sour soils. 



Ever since the day of Unger and Thurmann, there has been consider- 

 able difference in opinion regarding the relationship between soil acidity 

 and vegetation. A grouping together of plants into societies, doubt- 



