Som Reactions oF Certain FErns—I 19 
The complementary term ‘‘alkaline soil plants” is 
unsuitable for those showing dominant reactions toward 
the right hand side of the table, since the degree of alkal-. 
inity represented is at most but slight, and moreover no 
species of this class has been found which will not grow 
also in neutral and even slightly acid soils. The evi- 
dence indicates that the important factor in the case of 
plants avoiding the most acid soils is the relative abun- 
dance of calcium compounds, and accordingly “calcar- 
eous soil plants” will be used. The terms ‘“‘calciphile”” 
(lime lover) and ‘‘calcicole” (lime grower) are often ap- 
plied to this class of plants. Since plants may grow in 
calcareous habitats for various other reasons than “love 
of lime”’ the latter term is the preferable one; but neither 
is really necessary. This class is marked in the table by 
a C, for calcareous. 
It is evident from the table that no sharp line can be 
drawn between the two classes, as marked overlapping 
occurs in the central columns, especially in those of 
specific acidity 30, 10, and 3. Laboratory tests for 
calcium compounds have shown these to be present in 
practically all the soils concerned, their amount and 
especially their solubility diminishing markedly as the 
reactions approach mediacidity. By no means all spe- } 
cies showing calcium compounds in their soils are calcar- 
eous soil plants; for when. the specific acidity exceeds 
about 30 the physiological effect of the acid appears to 
predominate over that of the calcium; and although 
when the specific acidity is 10 or below, the effect of the 
calcium is dominant, some acid soil plants can still thrive 
even at the neutral point. In soils termed minimacid, 
plants of both classes may flourish side by side; but if 
enough occurrences of each species can be studied, the 
dominant reaction is always found to lie definitely to- 
ward one side or the other, and the plant can be assigned 
to the corresponding class. 
