Relation to Chalk and Mineral Salts. 83 
demonstrated for species of markedly different acidities, it is not possible in 
practice to follow it out in fine detail. 
(b) The theory that the toxic action of chalk is due to saturation of 
the Sphagnum acids, and subsequent derangement in metabolism, does not 
appear probable in view of the various experiments and observations quoted. 
If the saturation acts directly, it is difficult to see why high concentrations 
should kill the highly acid species and not those with low acidity. And it 
is difficult to conceive the mechanism of an indirect action. The Sphagnum 
cannot feel the want of fresh absorbed base at once, for it is capable of 
living and growing in distilled water for a long time at the expense of 
previously absorbed base. A Sphagnum supplied with a fatal amount 
of chalk dies promptly, and shows no sign of attempting to manufacture 
a fresh quantity of acid compound by temporarily increased growth. 
The most powerful argument against this view is supplied by the 
behaviour of Sphagnum to salts. These too are capable of saturating the 
acids, but despite this many of them are supported in high concentrations, 
although they may be no better nutrients than calcium carbonate. Calcium 
sulphate was supported in all the species Paul tested, in concentrations up 
to 2,000 mg. per litre (= 1,400 mg. CaC 0 3 ). The case of calcium chloride 
is conclusive; it is no better as a food-stuff than the carbonate, and it is 
supported by 6*. medium up to 966 mg. per litre (= 880 mg. CaC 0 3 ). 
If we look for a more natural explanation, the most probable seems to 
be that it is by altering the reaction of the solution that the carbonate acts. 
Sphagnum can grow best in an acid medium, which it cannot obtain in the 
presence of chalk. The ability to withstand high concentrations of chalk 
would then be an ability to withstand strong alkaline reactions. The 
behaviour of Sphagnum to acids and alkalies provides a means to test this 
hypothesis. 
The acids and alkalies chosen—hydrochloric and citric acids, and 
sodium hydroxide and sodium bicarbonate—could scarcely stimulate 
growth by supplying mineral nutrients. The results are given in Tables 
VIII and IX. 
Table VIII. 
Growth of Sphagnum 
Concentration 
contortum . 
recurvum. 
rubellum. 
of alkali. 
NaOH. 
Of 
NaHCO z . 
NaOH. 
NaHCO z . 
NaOH. 
Of 
NaHC 0 3 
°/ 
N/250 
A 
7 
/o 
7 
% 
0 
% 
13 
0 
lo 
0 
N/500 
85 
62 
0 
15 
0 
0 
N/750 
9 ° 
7 ° 
0 
1 5 
0 
0 
N/ioco 
63 
66 
0 
20 
0 
6 
N/2000 
70 
64 
62 
38 
20 
26 
N/3000 
100 
88 
70 
70 
26 
33 
N/5000 
80 
93 
93 
73 
106 
116 
