74 Skene . — The Acidity of Sphagnum and its 
comparison with Table II. Paul prefers the former method of statement, but 
does not show experimentally that the toxic effect of the chalk takes place 
when a certain amount is supplied, rather than when a certain concentration 
of the solution is reached. 
On the hypothesis that the presence of the humus acids is largely 
responsible for the supply of mineral nutrients, Paul argues that the 
Sphagna, which inhabit stations where the supply of salts is very low, will 
contain the largest quantities of these compounds. This is so : 5 . ruhellum , 
the typical high moor Sphagnum , stands first, and the degree of acidity falls 
away in species which inhabit more favoured stations. The effect of 
the chalk is to neutralize the acids and render them incapable of absorbing 
further mineral supplies. In the high moor species, which are most 
dependent on their acids, this interferes more intensely with the normal 
metabolism of the plant, and these species are consequently the more 
sensitive. 
The experiments to be described were commenced on the publication 
of Baumann and Gully’s memoir, with the intention of trying over some 
of their results, and were subsequently extended to include some aspects of 
the work of Paul. 
I. Liberation of Acids from their Salts. 
This fundamental effect is very readily demonstrated. It is only 
necessary to soak a few shoots of Sphagnum rubellum for a few hours in 
a solution of any salt—say 5 per cent. NaCl—and then to test with methyl 
orange : a strong acid reaction is always obtained. A control with distilled 
water always gives a negative result with methyl orange, though a slight 
reaction may be obtained with litmus; as this is reversed on boiling, it may 
be taken as due to the presence of carbon dioxide. 
That the acid present in the treated salt solution is the acid of the 
salt employed is not so easily demonstrated. The following method is 
fairly conclusive. Solutions of copper chloride of 0*5 %, o*i %, 0-05 %, 0*035 %, 
are employed ; of each 100 c.c. is allowed to stand overnight with about 
5 grm. (moist) of Sphagnum. Each solution is then tested with ammonium 
hydroxide, and the colour produced compared with that given by control 
portions of the original solutions. It is found that the colour given by the 
stronger solutions is much weakened, by the two weaker almost if not quite 
gone. If the chloride be tested for with silver nitrate, then the amount 
of the precipitate is found to be the same before and after treatment. 
A large amount of copper has thus been removed, while the acid radicle is 
present in undiminished quantity and the solution has acquired a strong 
acid reaction. The presence of copper in the Sphagnum may be demon- 
