16 AMERICAN FERN JOURNAL 
relationships. The first plan tried was to carry samples 
from the field to the laboratory, and there determine 
the percentage of calcium oxide (lime) present, both the 
total amount, and the soluble portion; and a brief ac- 
count of some results thus obtained has been published.! 
Subsequently it has proved possible to work out a me- 
thod for measuring, in the field, the soil reaction (acidity 
or alkalinity) ;? and as this is much simpler, as well as 
more instructive, than the determination of lime, an 
extensive series of such observations has been made, 
which it is the purpose of this paper to record. 
The writer’s field work on rock ferns has extended 
from Vermont and New Hampshire on the north to West 
Virginia and Virginia on the south, and all of the com- 
mon species, as well as a few of the rarer ones, occurring 
within these limits have been studied. The results ob- 
tained are presented in table I, and subsequently dis- 
cussed in detail. The correctness of previous classifica- 
it is the soil rather than the rock which affects the growth 
of plants; acid humus sometimes coats limestone ledges 
usually more or less acid in reaction, alkaline (calcareous) 
soils may accumulate on these rocks through the decom- 
position of vegetable debris, and typical calcareous soil 
species thrive there. Accordingly, actual tests have 
been made of the soils at the roots of the plants investi- 
gated. It is probable that further work will result in 
extending somewhat the ranges of reaction here recorded, 
although it seems unlikely that the classification of 
‘American Fern Journal, 7, 110-112, 1917. 
*To be published in Journ. Wash. Acad. Sci., April, 1920. 
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