SOIL ACIDITY WHERRY. 



Table 8. — Soil reactions of 07-chids — Continued. 



265 



Name (Gray nomenclature). 



LISTERA GROUT. 



(Twayblade orchids.) 



Listera convallarioides 



cordata 



australis 



sinallii 



LIPARIS GROUT. 



(Blade-lip orchids.) 



Microstylis monophyllos 



Liparis liliifolia 



Loeselii 



Microstylis unifolia 



APLECTRUM GROUP. 



(Chain-bulb orchids.) 



Calypso bulbosa 



Aplectrum hyemale 



Tipularia discolor 



CORALLORRITIZA GROUP 



(Coral-root orchids.) 



Corallorrhiza triflda 



WiFteriana , 



odontorhiza , 



maculata 



Num- 

 ber of 



tests. 



c 



A 

 AA 

 AA 



As with the ferns, the favoring of the more alkaline soils by the 

 more northern species and of the more acid soils by southern ones 

 is more or less distinctly brought out by this tabulation. There 

 are, it is true, a number of species of northern range with prefer- 

 ence for acid soils, but on the other hand all of those favoring cir- 

 cumneutral soils are northern; and without exception the southern 

 species grow best in acid or extremely acid soils. The explanation 

 is no doubt the same as in the case of the ferns, namely, that many 

 species now called northern are those which occupied the circum- 

 neutral soils left by the retreat of the great glacier in the northern 

 part of the continent. Other northern species may represent later 

 arrivals, acid soils having developed meanwhile; but southern re- 

 gions have never offered sufficient areas of circumneutral soil for 

 species to become adapted to such soils there. 



