594 wherry: reactions of soils 



alkaline, so that this habitat is comparable with the preceding 

 one. On the other hand, the same two species have been found 

 elsewhere growing in brown woods soil over noncalcareous rocks, 

 exhibiting a distinctly acid reaction, although in no case where 

 the plants appeared to be in a flourishing condition was the 

 intensity greater than 100. In so far as the data admit of 

 generalization, then, it may be stated that the showy orchid and 

 the 3^ellow lady's slipper prefer habitats in which the reactions 

 do not extend far to either side of the neutral point. 



Acid intensities ranging from 1 (neutrality) to 100 are shown 

 by the brown soil of open woods, in which thrive so many orchids, 

 such as Apledrum, Corallowhiza, Epipactis, some Habenarias, 

 Liparis, some Pogonias, Tipularia, etc., and by the clayey soil 

 in damp to dry meadows, supporting other Habenarias and many 

 species of Spiranthes. 



Bogs and swamps in noncalcareous regions show as a rule an 

 acid reaction throughout. The spring water supplying them 

 may be neutral or weakly acid, carbon dioxide producing for 

 instance an intensity of 3 ; in other cases the water may have an 

 intensity of as much as 300 just as it emerges from the earth, 

 perhaps owing to the presence of traces of sulfuric acid formed 

 by the oxidation of pyrite contained in the strata. But what- 

 ever the intensity of the water originally, the organic acids 

 formed by the decomposition of the accumulated vegetable 

 matter frequently attain an intensity of about 300, which, it 

 ma}^ be noted by way of comparison, approximates that of 

 acetic acid, M^hen half neutralized by a strong alkali. Calo- 

 pogon pulchellus, Habenaria flava, Pogonia ophioglossoides, Spi- 

 ranthes cernua, S. odorata, and rarely other species, have been 

 observed growing directly in the water of such swamps. 



The case of Cypripedium acaule is rather peculiar, in that it 

 show^s a different soil preference from the other species of this 

 genus. It has been found in sandy open woods, where the 

 intensity of acidity proves to be 100 to 300. An associate in 

 these surroundings is Spiranthes beckii. In pure rotted pine 

 needles, in which the reaction covers the same range, it grows 



