8 4 
Skene .— The Acidity of Sphagnum and its 
Table IX. 
Growth of Sphagnum 
Concentration 
contortum. 
recurvum. 
rubellum. 
of acid. 
HCl. 
HCit. 
HCl. 
HCit. 
HCl. 
HCit. 
N/250 
% 
0 
/o 
49 
% 
0 
% 
93 
0 
% 
80 
N/500 
13 
100 
40 
107 
0 
87 
N/750 
32 
124 
5 i 
142 
33 
93 
N/1000 
92 
124 
64 
127 
85 
100 
N/2000 
118 
113 
118 
118 
103 
106 
N/3000 
136 
142 
131 
147 
127 
114 
N/5000 
123 
122 
131 
H 7 
155 
109 
The results are a little irregular. We may, however, draw from them 
the following conclusions : 
(a) contortum is but little injured by hydroxide of N/500 or less, for 
recurvum the concentration is N/3,000, and for rubellum N/5,000. The 
same holds good for the bicarbonate, except that it is rather more favourable 
than the hydroxide for recurvum . These alkalies act, then, in precisely the 
same manner as does chalk. 
( b) For all three species hydrochloric acid ceases to be harmful at 
between N/1,000 and N/3,000, citric at N/500. At lower concentrations 
both acids exercise a very decided stimulating effect on growth. 
Taken alone, the results with alkalies may be interpreted in the sense 
of Paul’s hypothesis—in fact, he does quote experiments with alkalies in its 
support. But in conjunction with the stimulatory effects of acids in low 
concentrations, they afford good grounds for assuming that the harmful 
effect of chalk and the alkalies lies in the fact that they deprive the Sphagnum 
of the acid reaction which is beneficial to it. 
The method by which Sphagnum obtains its supply of nutrient bases 
entails the liberation of the acids of the salts concerned ; consequently the 
Sphagna are normally bathed in an acid solution. The reaction was at first 
an accidental accompaniment of another process, but it has now become 
a necessity for the Moss. Those species living in stations where the salts 
(and consequently usually also chalk) are scarce require a large quantity 
of acid compounds; they are doubly secured from ever encountering an 
alkaline reaction. Those inhabiting the more favoured low moors, both 
because they are less acid, and because chalk is more abundant in their 
environment, have more chance of being subjected to the influence of 
a neutral or alkaline medium. It naturally follows that the former are 
more sensitive than the latter. In some such way can we account for the 
connexion between acidity and sensitiveness. Be that as it may, it would 
seem that the preference of Sphagnum is for an acid reaction, its repugnance, 
in the case of chalk as in other cases, for an alkaline one. 
