wherry: reactions of soils 593 



of acidity or alkalinity, and this is continued until either an 

 intermediate color of one indicator, or opposing extremes of two 

 overlapping ones, are obtained. 



The soils supporting the growth of all of the commoner species 

 of orchids native to the east-central states have been studied 

 by this method, about 200 soil samples, collected as close to the 

 roots of the plants as possible, having been examined. The 

 results can best be expressed by describing first the relations 

 found to exist in the different types of habitat, taken up in the 

 order of increasing acidity. 



In swamps in limestone regions the reaction of the standing 

 water and of the underlying soil may be distinctly alkaline, 

 because of accmnulation of calcium bicarbonate. This sub- 

 stance in saturated solution may show an alkahnity of 100 or 

 more, but in bogs supporting the growth of orchids it appears 

 never to be sufficiently concentrated to exceed the alkaline 

 intensity of 10. The only orchids which have been noted as 

 growing in a soil with such a reaction are the tall Cypripediums, 

 C. candidum, C. hirsutum, C. parviflorum, and the variety pubes- 

 cens. The writer has not had opportunity to carry his stu- 

 dies north of Pennsylvania, but several more northern species 

 are reported to grow frequently or exclusively in calcareous, 

 (or ''marly") bogs in which the reaction is no doubt similar 

 to that here noted; these include Calypso hulbosa, Habenaria 

 dilatata, H. hyperborea, Microstylis monophyllos, and Spiranthes 

 romanzoffiana.^ 



Calcareous (alkaline) soils may also develop in woods above 

 limestone rocks, so it seemed interesting to inquire if the same or 

 related species of orchids might grow in such situations. Two 

 instances have been brought to the writer's attention, Cypri- 

 pedium parviflorum and Orchis spectabilis, growing in black soil 

 full of limestone chips a mile southwest of Allentown, Pennsyl- 

 vania.^ Tests of these soils showed them to be in fact slightly 



° This list has been compiled from articles by Prof. M. L. Fernald and others 

 scattered through the journal Rhodora for several years past, supplemented by 

 a private communication concerning occurrences in New York kindly sent by 

 Prof. K. M. Wiegand. 



^ These were located bj' Mr. Harold W. Pretz of Allentown. 



