Relation to Chalk and Mineral Salts. 
77 
Sphagnum contortum , with an acidity of 0*0276, gives a weak but very 
distinct reaction with salt; while Fontinalis , with an acidity of 0-0414, gives 
only a very faint reaction. This would seem to indicate that while S. con - 
tortum is more efficacious than Fontinalis in breaking up salt, the reverse is 
the case with calcium acetate. 
The qualitative test with sodium chloride is not delicate, and all further 
tests were made quantitative with calcium acetate. These were not confined 
to the Mosses. Wieler (T 3 ) states that the properties of Sphagnum are 
exhibited by the cell-walls generally of vascular plants. Confirmation of 
this was desirable and was obtained. The results are set out in Table V. 
In the cases of those plants marked x a control experiment was carried 
out, using distilled water. In every case the water was neutral at the end 
of the experiment. This disposes of Arndt’s suggestion that the acidity 
in these cases is due to soluble organic acids originally present in the 
plants. 
Table V. 
Plant. 
Parts tested. 
Acidity. 
Dicranum scoparium . 
°'° 54 I 
Fontinalis antipyretica 
0-0414 
Neckera complanata 
0-0367 
Mnium hornum . . 
0-0310 
Polytrichum commune 
0*0299 
Evernia prunastri 
0-0588 
Fagus . 
dead leaves x 
0*0345 
Pinus . 
dead needles x 
0-0230 
Ptens . 
dead fronds x 
0-0230 
Air a . 
dead stems and leaves x 
0-0195 
Calluna . 
dried shoots x 
0-0149 
Orchid air roots (sp. not known) 
0*0172 
Wieler states that cellulose as cotton-wool, and as a preparation from 
wood, is also acid ; I tested cotton-wool and filter-paper several times with 
uniformly negative results. It is scarcely conceivable that they should be 
able to absorb bases from salts, and could they do so our entire chemical 
data would stand in need of revision ! 
The acidity of Sphagnum is on the average 0-07, so that most of the 
other objects tested are less active, and lie in or below the region of 
the less active species of the Bog-moss. 
The acid properties are widely distributed throughout the vegetable 
kingdom, and to them is certainly to be attributed the acid nature of humus. 
The action of chalk on the soil, besides the direct neutralization of acids 
therein, will be to saturate the acid compounds of the plant remains and so 
to prevent them breaking up salts in the soil solution ; that is, it prevents 
the souring of the soil indirectly as well as directly. It need scarcely be 
mentioned that the presence of such compounds in the roots may have 
a most important bearing on the absorption of mineral nutrients. 
